MacOS 27 will solve System Data bloat???

You should aim to have 15-20% of your total internal storage as free space (~20-25 GB as an absolute minimum). If you do not have enough free space on your Mac’s internal storage, then here are some steps to take to safely free up space:

Free up storage space on Mac - Apple Support

Optimize storage space on your Mac - Apple Support

How to free up ‘System Data’ and other st… - Apple Community

"System Data" comprises your data, but they are typically hidden files that Spotlight cannot assign to a specific category like Documents or Applications. Examples include Outlook attachments, iOS updates, Cloud storage caches, etc. Starting with macOS 27 Golden Gate, System Data also includes what macOS used to call ‘purgeable’ storage – system caches, Time Machine snapshots and some other data, though the user had no control over the purging. That means macOS 27 makes System Data bigger, not smaller.

Trying to manually clean out hidden files in System Data is likely to cause more problems than it solves, macOS hides those files for a good reason. Follow the steps in the linked articles above. 

On macOS 27, separate ‘purgeable’ space is no longer reported, and instead those data are now considered as used space. They are also now included in System Data, accounting for the apparent increase you would see. You won't lose space, macOS just categorizes things differently than on Tahoe.

More detail on this change in this User Tip:

System Data and Free Space Changes in Gol… - Apple Community

The best advice is to just ignore the System Data category. ‘System Data’ is merely a catch-all category for files that Spotlight cannot assign to specific categories like Applications, Documents, Photos, etc. In fact, what is now shown as System Data used to be reported as ‘Other’, Apple changed the label in macOS 12 Monterey. System Data probably sounds better, but Other was closer to reality. 

mhb wrote:

I have a big problem with System Data bloat. I have a 500 GB drive on a 2020 Macbook Air running the latest MacOS 26 version, and 220 GB is System Data. I've tried to get that down using the various tips provided online but nothing has worked, including starting up in Safe Mode, deleting cache and logs ...

That is because in many (not all) cases, "System Data" can be mostly your own files, that Apple doesn't have an easy way to categorize, as others have pointed out. You can figure this out if you obtain a utility like Stereograph or DaisyDisk (I have both, these each do require a small payment but it may be worth it if you have 220 GB (40% of your disk) and don't know what it is. Those utilities drill down and will find and identify everything on your drive.

By the way, your use of the term "Bloat" is interesting. In many cases, this "System Data" includes files that the user has created from the apps or software that they use.

I asked about this at the Apple Store last evening and was told that if I download MacOS 27 it will clear out the System Data bloat. Can anyone confirm that's the case? I know just updating within the current MacOS 26 keeps all that bloat. Is it different when downloading a whole new OS?

I don't believe that what you were told is correct.

I'm at the point where I'm wondering if I need to get a new computer and drag my files over and reset my preferences and start over (ugh), but if just updating to MacOS 27 will help, I'd rather wait on the new machine. Thanks.

Well, I don't think that will work if you drag back over all your files as that would simply bring all that "System Bloat" over to the new computer. It could become an expensive undertaking that does not help you in your use of disk space.

I have several Macs in use and "System Data" ranges from 40 GB to 100 GB on these Macs, which are on OS from Monterey to Tahoe. The MacOS itself on one of the Tahoe machines takes about 20 GB.

mhb wrote:

I've tried to get that down using the various tips provided online but nothing has worked, including starting up in Safe Mode, deleting cache and logs ...

Not surprising. The internet's not true. Deleting cache files and logs will have no impact other then slowing down your computer.

I asked about this at the Apple Store last evening and was told that if I download MacOS 27 it will clear out the System Data bloat. Can anyone confirm that's the case?

It is not the case.

I know just updating within the current MacOS 26 keeps all that bloat. Is it different when downloading a whole new OS?

Installing a new OS will only make it worse.

As neuroanatomist describes, there were some changes in macOS 27 regarding storage. But these changes only affect how the storage is displayed. I've seen a number of people post on this forum being upset that they installed macOS 27 and lost a lot of free storage. But it turns out that macOS 26 simply wasn't being truthful. They never had that much free storage to being with and macOS 27 is being a little more honest about it - but only a little.

I'm at the point where I'm wondering if I need to get a new computer and drag my files over and reset my preferences and start over (ugh), but if just updating to MacOS 27 will help, I'd rather wait on the new machine.

With a 500 GB hard drive, you should be able to get storage to a manageable level. Usually this problem is caused by running out of free storage. Note that neuroanatomist says that 20-25 GB is an absolute minimum. Most people reading that will take it the wrong way. You need 100 GB of free storage for optimum performance and reliability. Once you get down to 50 GB free storage, you'll start to experience performance problems and this "System Data" bloat.

25 GB is enough to download a new version of the operating system. That's all most people care about these days. They're addicted to these updates. But 25 GB is an absolute minimum. It would deliver a very poor experience. You want 100 GB free. Since you're still running macOS 26, what you're seeing as "available" storage isn't free. In macOS 26, "available" is still a fantasy. Most likely you are simply out of free storage.

You'll need to download a 3rd party storage management tool to get control over it. I can't recommend one because I develop one and I'm not allowed to post a link to it. If I thought the other storage management tools were great, then I wouldn't have written my own in the first place.

You need to see which of your folders is taking up too much space, and delete the files that are causing it. Hopefully, these are your files to delete and you can simply copy them to an external hard drive for safekeeping. If the files are in some hidden system folder, then I recommend asking here before touching them. Some files aren't safe to delete and people tend gravitate towards those options that do the most damage, for the least impact.

steve626 wrote:

I have several Macs in use and "System Data" ranges from 40 GB to 100 GB on these Macs, which are on OS from Monterey to Tahoe. The MacOS itself on one of the Tahoe machines takes about 20 GB.

If/when you update a Mac to Golden Gate, System Data will very likely increase. On my personal Mac (16" M4 Pro MBP, 2 TB internal storage), System Data ranged from 9-40 GB before upgrading that Mac from Tahoe to Golden Gate. On Golden Gate, System Data ranges from 120-160 GB. So I can see where the term 'bloat' seems applicable.

It's not, technically. Still the user's data, macOS just changed the accounting method for space calculations ('purgeable' space is not separately reported, those data are now counted with System Data).

I have the same issue, basically my MacBook Pro is now unusable....

Having a large amount of System Data is the symptom. The problem is your drive is too full, probably so much so that removing anything will take a long time to clear. System Data is almost always your data (or Time Machine local snapshots). It is not the OS or any parts of it. That is all on a separate volume. There have been some runaway cache data that people have found. You need to use a disk space analyzer to figure out what is taking up large chunks of data. I like GrandPerspective because of its graphical representation. Even with one of those apps, you will not find anything labeled "System Data" because it isn't a thing. It's a made-up category to collect things that Spotlight could not identify as belonging to one of the other categories listed in that incredibly useless "Storage" display. Nothing will resolve "System Data bloat" because it isn't a thing.

No, 27 does not resolve System Data bloat. I just finished rebuilding my M2 Studio from scratch (not Time Machine) and, once completed, the System Data size was the same as before. Unlikely a new computer will solve the problem.

I'm going to follow @neuroanatomist's advice and ignore the problem. I've got bigger fish to fry.

mhb wrote:

I appreciate the help so I can understand all this better. You can see my reply to neuroanatomist for an update. I definitely want more free storage than 20-25 MB. What's most frustrating is that I read that System Data should only be, say, less than 25 GB

That is the size of the macOS system and is accounted for elsewhere. “System Data” is not the OS and may not even be “system” data. It will fluctuate and there isn’t any size metric you can hang your hat on. As neuroanatomist already described, the System Data category is a catch all for things Spotlight doesn’t recognize or does not fall into the other Storage categories. It was actually once called “Other,” but that was too confusing so they renamed it “System Data.” Clears it right up, doesn’t it?

The “system” data that usually takes up most of the space is local Time Machine snapshots. That builds up if you have a Time Machine backup that you don’t backup to regularly.

Another common problem with clearing storage is deleted files. SSD’s cannot make deleted space available instantly. It may take overnight to reset the storage to make it writable. That process is slowed if you have little free space. “Free” and “Available” are not the same. Free is a subset of Available. The free space can be seen in disk utility. If you have very little free space, pick a few large things to delete that are smaller, in total, than the free space, then leave your Mac on and go to bed. Hopefully the deleted space will be reset in the morning and you will have more free space.

No it won't I updated to Mac OS27, I did and now I have 250gb of system data and Apple can't help or are able to get rid of it, in fact they say it's not a problem. I only have 100gb left on my Hard drive.

mhb wrote:

What's most frustrating is that I read that System Data should only be, say, less than 25 GB

Where did you read that? The internet? The internet's not true.

System Data should be whatever is appropriate for your computer. Every computer is different.

The most important thing to remember here is that "System Data" is simply a field on that atrocious System Settings > Storage display. Don't even go there. It's worse than useless. All it does is confuse people. This screen isn't what people think it is.

Primarily, this is a Spotlight aggregator. Spotlight searches your computer and categorizes each file as "something" - documents, videos, books, mail, messages, music, etc. Only there is no "etc". That's "System Data". Much of the data put into this category may have nothing whatsoever to do with the operating system.

For example. I'm a developer so I have lots of relatively unusual software. I also have a "Developer" category for 15 GB. But I have some virtual machines installed too. Those account for part of my 106 GB System Data. For me, that's perfectly normal.

I haven't seen anything so huge that it will make a difference if I delete it

But do you know where to look? Most of this data is in hidden directories. There are many, many hidden directories on your computer. There's nothing that Apple likes more than hidden directories.

so it must be large amounts of small files

It is not.

I can't freely delete without potentially causing issues. Or, likely, I'm still missing something basic.

All I can do at this point is refer you to what I've already posted. Every computer is different. If anyone on the internet tells you with any confidence that it's definitely X, Y, or Z, they are definitely lying to you. The operating system has become hopelessly complicated. Your hard drive is unique in the universe. They say that every time you shuffle a deck of cards, the order is unique in all of existence. There are 52 cards in a standard deck. There are hundreds of thousands of files on your computer.

I have 170GB of System Data bloat with over 225GB of free disk space on macOS 27.0.1, so it just bloats regardless. And mine is brand new, only 10 days old. That only shows when my external SSD is plugged in. Immediately after ejecting it, System Data drops to 67GB.

Apple engineers advised me that macOS is creating one snapshot in case my external APFS drive becomes corrupt or isn’t ejected properly. They ran full diagnostics, and that’s what they reported back to me.

So according to them, it’s completely normal, but IMO, it’s ridiculous. They could easily fix this, or maybe they just aren’t smart enough to properly label everything and be transparent. Who knows? 😂

It’s annoying, and yes, it’s purgeable space, but you shouldn’t have to buy a brand-new computer only to have macOS automatically take up a huge chunk of your storage and then basically say, “Well, you can have it back once your hard drive starts running out of space.”

I think that’s ridiculous. That’s just my opinion, though.

melvin3v wrote:

In my case, CleanMyMac and DaisyDisk were unable to locate the hidden System Data.

CleanMyMac can be poison for Macs. I would uninstall that completely, and then search for leftover remnants and delete those as well.

Tools like DaisyDisk or Stereograph won't find anything called "System Data." That is an accounting label Apple uses for a wide range of items. No folders are actually called "System Data." However those tools will enable you to track down where every bit of your used file space is on your Mac. Including space used on the internal drive as well as on the external drive.

I migrated from an M1 MacBook Air with only a 256GB SSD annd 109gb free and there’s hardly anything on either computer. My Mac mini has a 512GB SSD with about 225GB free, yet System Data jumps to around 165GB whenever my external SSD is plugged in. As soon as I unplug it and reopen Storage settings, System Data drops back down to around 60GB.

So with 512 GB SSD and 225 GB free, you are using 287 GB on that drive. Is that what you expect? If you expected to be using less, use DaisyDisk or Stereograph to do an audit to find out exactly where your disk space is going. Then you can decide what to do about that. Be careful before deleting system files or files in hidden directories, however.

CleanMyMac may have corrupted the internal accounting on the Mac so it is not clear to me if this is fixable without a complete wipe, clean reinstall, and then bringing over only files and accounts but no settings and no apps (reinstall the apps fresh).

rranger wrote:

For some bizarre reason beyond my comprehension, Apple makes a copy of the backup on the internal drive, which creates ridiculous amounts of "System Data." Why, I ask rhetorically, am I making an external backup if I want a copy on my Mac?

That's not how it works. Maybe you read this somewhere on the internet or in Reddit or got it from ChatGPT. But it's not correct and your post is perpetuating incorrect information. Apple does not make a copy of the backup on the internal drive. What is done is that, in between backups [which can be every hour, or some other interval, or less often if the user disconnects the backup drive(s) for a while], the Mac records changed files inside "snapshots" that are kept on the Mac while waiting for the next backup. This is so if you need a backup to recover a lost or corrupted file after the last backup was done but before the next one is run, it can be recovered from those interim "snapshots." Those snapshots are usually quite small -- one exception could be if massive files are being modified and are waiting to be backed up, such as virtual machine files or huge videos. So no, your Mac does not "copy the backup onto the internal drive," not at all. Those snapshots also help the next backup to run efficiently and quickly as they have done a lot of the "work" for the backup ahead of time. After the Time Machine backup is done, snapshots are deleted but then new ones get created as more files are created or modified in between backups.

tbirdvet wrote:

External drive increased my system data and I have no other items that would cause this. I made no changes between OS26 and OS27. I show a difference of >10GB with my external TB5 drive on vs off.

Is that external drive also being backed up along with the internal drive, to a separate Time Machine drive? If so, there may be snapshots being generated from that external drive's contents and those snapshots might be included in the "System Data" accounting bin.

It will not correct the Bloat issue..... Ive tried it.

In my case, CleanMyMac and DaisyDisk were unable to locate the hidden System Data. I migrated from an M1 MacBook Air with only a 256GB SSD annd 109gb free and there’s hardly anything on either computer. My Mac mini has a 512GB SSD with about 225GB free, yet System Data jumps to around 165GB whenever my external SSD is plugged in. As soon as I unplug it and reopen Storage settings, System Data drops back down to around 60GB.

Apple engineers told me this is normal behavior, which is frustrating. They were pretty firm in their explanation that macOS 27 creates a hidden snapshot in case the external SSD becomes corrupted or is improperly ejected. Whether that’s BS or not, I have no idea, but they spent a 3 days investigating before getting back to me with that explanation or that’s at least when supervisors responded 👍 And this is Os27 for me OP is on Tahoe I beleive.

So that’s been my experience, which is a little different from OP’s. Hopefully Apple can figure out a different method someday 😂 I would think with AI etc they could easily identify okay this is 3rd party cach, document then just show at least what type of files they are and if should remove or not even clean my Mac does that.

mhb wrote:

...I'm starting to think that they way I function in 2026 -- not just the browser -- is just going to require a lot more disk space for "System Data" than six years ago...

Again, "System Data" is just a catch-all for stuff Spotlight doesn't assign to a specific category. Spotlight itself is not perfect. On my work Mac, the cloud storage service we use keeps a local cache of 200 GB, and Spotlight adds that to the Applications total.

But it's very likely that you're going to require more storage today than you needed 6 years ago, and even more 6 years from now. That's the way technology works.

This is Get Info on a RAW image from my camera:

One picture, it's a 28 MB file. This is the type of Mac that I used from 1987 to 1993:

The red box highlights that instead of the base model with two floppy drives, I sprung for the upgraded model with a 20 MB hard drive. What could store an operating system, lots of applications and thousands of files decades ago couldn't hold a single picture that I take today.

The alternative is getting a software program to help, which can be a bit of a crapshoot if you're not familiar with these and some are dodgy.

What you need to manage are the things you can easily manage – photos, videos, music, email and text message attachments, etc. Trying to manage cache files, profiles, etc., is a useless exercise in frustration.

Since you cannot add internal storage to most Macs, buy more than you think you'll need at the outset. Then manage as you go. I have a 227 GB Photos Library and 300 GB of 'Documents' (of which 150 GB is actually my iMovie Library, and a lot of the rest are RAW images, which Spotlight calls documents not photos). Most or all of that could be moved to external storage. For example, I only keep a couple years of RAW images on my Mac, the several hundred GB of older ones are stored externally. Since I got this Mac with 2 TB of internal storage, I have plenty of space.

My System Data didn't change over night after all that material removal yesterday.

The intent there was to clear more free space, not necessarily reduce system data. Did your free space increase? How much free space do you have as indicated in disk utility?

have you attempted to remove the time machine snapshots from disc utility?

Wasn’t true for me I just worked with Apple support for a week regarding system data bloat on brand new Mac Mini. Mine kept climbing by 10gb daily up to 167gb system data on a 512gb SSD it’s maddening. They said it’s fine and supposed to do this? everytime I plug in non Time Machine external ssd system data climbs to over 160 and when I unplug it drops to 60gb I’ve never experienced this but it’s frustrating to buy brand new system and for Mac to take hostage 100gb IMO.

This is now a few days old, and I don't know whether you're still looking at this, but the biggest problem with macOS, IMHO, is the way that Time Machine works. When I first got my Mac, I let Time Machine do frequent backups to an external drive. For some bizarre reason beyond my comprehension, Apple makes a copy of the backup on the internal drive, which creates ridiculous amounts of "System Data." Why, I ask rhetorically, am I making an external backup if I want a copy on my Mac? Bizarre! The best solution is to set Time Machine to manual backups and - when complete - immediately go into Disk Utility and get rid of the duplicate on the internal drive. I was able to regain many GBs of space that way, and still have the external backup. I hope this helps with your situation.

Ask Gemini, Claude, or ChatGPT how do this and you'll get clear instructions.

Interesting thing happened after reading many replays over the past month with System Data, I ejected my two hard drives after reading some peoples Data went down and mine went from 250GB to 90 GB just by ejected them.

This might be a somewhat obvious solution to OP's post (that was me), but one day I just hunkered down for about three hours and purged countless old files from my hard drive that I no longer needed, some up to 20 years old. I knew I had freed up a lot of space, but I just happened to look at my storage data, and I now have 164 GB "free space" on my 500 GB hard drive (I think it was less than 100 before) and only 123 GB "system data." That's still high for "system data" by some users' metrics, but it's 100 GB less than before, so I'm quite content ... and not carrying around so much digital baggage. I haven't installed OS 27 yet, but I'm glad I did this spring cleaning first.

Barney-15E wrote:

“Free” and “Available” are not the same. Free is a subset of Available.

Actually, in macOS 27 'free' and 'available' are the same. macOS no longer treats 'purgeable' data as part of available space, which was the reason for the difference in macOS 26 and before.

mhb wrote:

I almost never clear histories etc. But when I just cleared the history and extensions of my most used profile, precious little changed in System Data.

Remember that "deleted" files are a big source of "System Data". It will take the system a day or two to purge deleted files. So don't expect any immediate relief from deleting files. If anything, your System Data will increase.

I'm starting to think that they way I function in 2026 -- not just the browser -- is just going to require a lot more disk space for "System Data" than six years ago, unless I want my life to become about computer maintenance. So I'm back to considering a new computer with a tedious, manual, clean install of apps, profiles and preferences on a 1 TB drive for the next six or so years. Maybe this is something many are dealing with, whether they know it yet or not.

I would consider a 1 TB to be a minimum for any kind of professional usage. I keep 100 GB free and I don't have any problems.

The alternative is getting a software program to help, which can be a bit of a crapshoot if you're not familiar with these and some are dodgy.

Hopefully mine doesn't look dodgy.

melvin3v wrote:

If “System Data” is meaningless, what’s the point of showing it?

Not my call.

just go to Reddit and type in System data lol!

Thanks for the suggestion, but I'll pass.

Why hide what’s taking up that space instead of showing us what can safely be removed? Telling us to ignore it doesn’t solve the problem.

We can't do anything to solve a problem involving something that someone else (like Apple) is doing or saying. We can only control our own response to it.

Hence my suggestion to ignore the display where Apple is saying the most outlandish things. It's really not too different than social media. If you find a place where people are making the most outlandish, unhelpful, and hateful comments, don't go there anymore. Or if you do, try to avoid known sources of harm and misinformation.

And regarding your last line about fixing low storage: I currently have over 200 GB free.

Then you're good. There's nothing else you need to do. I try to keep 100 GB free. That gives me a nice buffer from the danger zone of > 50 GB where performance starts to suffer.

I’m questioning why another 167 GB is lumped into a catch-all category I can’t meaningfully manage. That’s a lot of space, especially when I have zero iOS backups and found no local Time Machine snapshots when checking in Terminal.

If macOS is supposed to manage that space automatically, why can’t it explain what it’s keeping and why? How about some transparency instead of “trust me, bro”? 🤷🏼‍♂️ Just my thoughts 👍🏻

I cannot provide any transparency. I don't work for Apple. All I can do is provide my own thoughts. All you can do is trust me, bro. 😄

It does seem like Apple's approach is that the user paid for this storage, unused storage is wasting the user's money. That's definitely the case with RAM. That approach was a significant problem about a decade ago when it was first introduced. Back then, when an iMac hit swap space, it hit a spinning platter and it stopped dead in its tracks. With modern SSDs, it's all much smoother.

But that logic hasn't translated very well to storage. Running out of storage is much like running out of RAM without virtual memory. There's just nowhere else to go. Hoping to off-load some of that to the cloud is slower than a spinning hard drive and less effective.

I did develop an app to help people manage storage. There are a handful of similar apps, but only a handful, with a couple of fingers left over. I try hard to help people recognize which files can be safely removed. But that's also a hard problem. It's been many years since Time Machine local snapshots were a leading cause of storage problems. These days, it's all over the charts. Could be anything really.

melvin3v wrote:

I have 170GB of System Data bloat with over 225GB of free disk space on macOS 27.0.1, so it just bloats regardless. And mine is brand new, only 10 days old. That only shows when my external SSD is plugged in. Immediately after ejecting it, System Data drops to 67GB.

I don't know what else to tell you. System Data is a figment of Apple's imagination. It. Does. Not. Ex. Ist.

All indications are that it's some misnaming of "other data" from Spotlight's index. But that data is only (supposed) to pertain to the startup drive. This is the first I've heard of external drives being involved. I'm not saying you're wrong. I've seen several reproducible bugs that other people couldn't reproduce. But all that being said, there are certain well-known aspects of certain technologies that strongly seem to contradict what you're describing.

Apple engineers advised me that macOS is creating one snapshot in case my external APFS drive becomes corrupt or isn’t ejected properly. They ran full diagnostics, and that’s what they reported back to me.

That's not true. For one thing, as I mentioned above, external storage doesn't apply. For another thing, snapshots themselves only consume a very negligible amount of storage - megabytes, not gigabytes. And finally, I have lots of external volumes. If what they said were true, I'd have snapshots all over the place. I have none.

What is the nature of this external drive? Is it used for Time Machine or a 3rd party backup. That might complicate matters. Perhaps that would confuse Spotlight. Spotlight is very easily confused. But again, we circle back to my first point. None of it exists. It's like people who get upset at the "Tauriel" character in "The Hobbit" movies saying she didn't exist. Well, none of them exist. It's a work of fiction, much like System Settings > Storage. The biggest difference is that Tolkien's stories are delightful fables that bring joy and entertainment to children and adults alike. The macOS Storage display - not so much.

It’s annoying, and yes, it’s purgeable space

Purgeable space does not exist.

How do I know this? There are many reports here in the forums of people trying to download a new OS update or perform some other kind of large-scale data operation. The operation fails because they don't have enough free storage. "But, but, but", they say, "it says I have 49 caboodles available! That means I must have at least 40 caboodles of purgeable storage." They tried some operation that needed 12 caboodles of purgeable caboodle storage and the operating system simply said, "no". Therefore, those caboodles weren't ever "purgeable", were they?

"Purgeable space" is another way of saying "used storage". If you need it for something, you can't have it. What else works this way? Used storage.

you shouldn’t have to buy a brand-new computer only to have macOS automatically take up a huge chunk of your storage and then basically say, “Well, you can have it back once your hard drive starts running out of space.”

I think that’s ridiculous.

It is ridiculous... because you can't have that storage back 😄.

All caboodle jokes aside, purgeable storage is used storage. It's used for things like caches that aren't strictly required. They simply speed up normal operation. You can delete them (well, not really). After a couple of days, if you try really hard, you might be able to make them go away and recover that precious 14 GB of storage that you need for that Oh So Precious operating system update. Yesssss. My precissoussss. (You see what you started? Bagginses stole our storage. Tricksy hobbittses! We hates bagginses forever.) You can't defeat the power of The One Ring forever. Sauron's deadly caches will regroup in the shadows, slowly, and one day, when you least expect it, burst forth from Minas Morgul with terrible new flame and gigabytes of usage.

But if you ever get tired of this fantasy, and desire a more solid grounding in reality, then stop looking at System Settings > Storage. It's not true. But can you handle the truth? The macOS file system is horribly complicated. You can dig into it and learn how it works if you want. Or you can take a shortcut with a 3rd party storage management tool. Or you can live behind the Storage looking glass if you really want that. One drive makes your storage big and one drive makes it small. And System Settings > Storage doesn't do anything at all.

Yup, see! I’m glad I’m not the only one experiencing this. I’ve been reporting the exact same behavior on macOS 27, and others on Reddit have confirmed it too. I love how some people on here insist this can’t happen. I said just wait until more people start reporting it! 😂

One question: Did you check Disk Utility to see whether that extra System Data was listed as purgeable space?

steve626 wrote:

That is because in many (not all) cases, "System Data" can be mostly your own files, that Apple doesn't have an easy way to categorize, as others have pointed out. You can figure this out if you obtain a utility like Stereograph or DaisyDisk

Yes. A few days ago my daughter asked in WhatsApp what to do when her 250 GB MBP was almost full (when we bought it she said there was no need for more storage than that in her light use...):

Safe boot did not help and there were no snapshots in Disk Utility (she uses CCC for the backups). I then advised her to download and check the disk with Omni Disk Sweeper:

She deleted those Xmind cache files and then had about 100 GB free space and could continue her studies.

Xmind User Guide: "You can clear file cache and remove temporary files and data stored by the app to free up space. You may clear file cache from File > File Cache > Select the file > Clear Cache."

https://xmind.com/user-guide/file-cache-new?highlight=cache

Thank you for taking the time to help. I had seen those links, and since my own material isn't only taking less than half my hard drive, I don't really want to focus on weeding that. But the link "How to free up ‘System Data’" helped quite a lot for me to understand how to find the larger folders and subfolders to look within to make the biggest difference. I spent about 2-3 hours doing this, careful to leave anything that I wasn't sure was just linked to an old application I no longer use. I also went through my email attachments and deleted Time Machine snapshots (there were only 2). After all this I was disappointed that my System Data only went from 220 to 194, still leaving only 134 GB "available" space.

I feel like I'm in a losing battle. I'm beginning to think I should just get a new computer and start fresh and tediously download my apps and transfer my files manually and reset all my prefs.

I appreciate the help so I can understand all this better. You can see my reply to neuroanatomist for an update. I definitely want more free storage than 20-25 MB. What's most frustrating is that I read that System Data should only be, say, less than 25 GB, which would leave me with plenty of storage and I wouldn't need to upgrade my system. I haven't seen anything so huge that it will make a difference if I delete it, so it must be large amounts of small files, but ones that I can't freely delete without potentially causing issues. Or, likely, I'm still missing something basic.

Actually, in macOS 27 'free' and 'available' are the same. macOS no longer treats 'purgeable' data as part of available space, which was the reason for the difference in macOS 26 and before.

That is interesting, but I thought mhb was still on Tahoe.

All this context is great and helping me digest the matter, I think.

My System Data didn't change over night after all that material removal yesterday.

What at this point is probably more of an aside than anything, this year I started using Firefox and have eight profiles set up, some with only a few tabs and some with many. I don't normally keep many open at once. I almost never clear histories etc. But when I just cleared the history and extensions of my most used profile, precious little changed in System Data.

I can definitely merge some of the smaller profiles and make them containers in one browser instance, and do better keeping the histories clean, but I'm starting to think that they way I function in 2026 -- not just the browser -- is just going to require a lot more disk space for "System Data" than six years ago, unless I want my life to become about computer maintenance. So I'm back to considering a new computer with a tedious, manual, clean install of apps, profiles and preferences on a 1 TB drive for the next six or so years. Maybe this is something many are dealing with, whether they know it yet or not.

The alternative is getting a software program to help, which can be a bit of a crapshoot if you're not familiar with these and some are dodgy.

Thanks everyone. I'm just going to get a new MB Air with a larger hard drive and manually transfer the files I need, reset prefs, etc. ... start "clean." I could use the larger 15" screen when I'm not at home too.

Wow. I guess I'm on the right track leaning into a new computer with a 1TB hard drive, so I will hopefully have a lot of cushion for the next six or so years. Are you still in the return window so you can get a bigger hard drive?

I did notice with OS27 that when I plug in an external drive it consumes about 16GB more of the system data. This is also different than with OS26. Seems like with every new OS more space is needed.

melvin3v wrote:

Wasn’t true for me I just worked with Apple support for a week regarding system data bloat on brand new Mac Mini. Mine kept climbing by 10gb daily up to 167gb system data on a 512gb SSD it’s maddening. They said it’s fine and supposed to do this? everytime I plug in non Time Machine external ssd system data climbs to over 160 and when I unplug it drops to 60gb I’ve never experienced this but it’s frustrating to buy brand new system and for Mac to take hostage 100gb IMO.

It's important to remember that "System Data" is absolutely meaningless. Anything you see on System Settings > Storage is meaningless. Don't look at it.

If you're running low on free storage, that's what you need to fix. But don't even look at nonsense.

If “System Data” is meaningless, what’s the point of showing it? Mine reports 167 GB, but Apple doesn’t give us a clear breakdown or a straightforward way to manage it. I’ve owned Macs since the PowerBook G4, and I never had this much space tied up like this on my older machines and it's the worst ive seen just go to Reddit and type in System data lol!

When we spend this much on a computer, having so much of the storage we paid for tied up without a clear explanation or control is frustrating. Why hide what’s taking up that space instead of showing us what can safely be removed? Telling us to ignore it doesn’t solve the problem.

And regarding your last line about fixing low storage: I currently have over 200 GB free. I’m questioning why another 167 GB is lumped into a catch-all category I can’t meaningfully manage. That’s a lot of space, especially when I have zero iOS backups and found no local Time Machine snapshots when checking in Terminal.

If macOS is supposed to manage that space automatically, why can’t it explain what it’s keeping and why? How about some transparency instead of “trust me, bro”? 🤷🏼‍♂️ Just my thoughts 👍🏻

etresoft wrote:

These days, it's all over the charts. Could be anything really.

That's the problem with using the Storage settings pane. Spotlight is good at finding a file for you, but bad at cataloging a disk. RAW image files are Documents, not Photos. The local cache for my work cloud storage data (200 GB) is Applications. Not to mention all the random stuff that Spotlight can't categorize and is lumped into System Data.

Preaching to the choir here, I know.

neuroanatomist wrote:

Spotlight is good at finding a file for you, but bad at cataloging a disk.

I would say it's better at cataloging a disk than finding a file. Spotlight will randomly fail to find specific files. I've got one folder that it refuses to index for some reason. I only found that by accident. How many other folders are mysteriously excluded that I don't know about?

But if you did, for some reason, what to categorize (almost) all of the files on your disk as applications, books, documents, images, messages, photos, and mail, the Spotlight will do a reasonable job of that. On the aggregate, it doesn't matter if Spotlight misses a few files or folders. It's just that this data isn't useful. So what if I have 493.2 MB of data in messages? How does that help with my 136.31 GB of System Data?

And System Data is even worse. I understand the need for an "other" category, but not with this name. It's like if you tried to use System Settings > Storage and asked, "why is my messages so big?" And Apple responds, "because you have so many Excel documents". But Excel documents aren't messages. Why aren't they classified as Excel documents? I've spent 3 days searching my messages and couldn't find any problem! And 5 years later, Apple still hasn't responded.

It just doesn't make any sense. It's not even internally consistent. It's like Apple is taking ownership of all "other" data on the computer through this name. These days, it's often (but not always) some 3rd party product causing the problem. So, understandably, people come here and ask why the latest "system" is so big. And we're left holding the bag trying to explain it to them.

Oh, now you've got me started....

I have 157 GB of free storage on this computer, so I'm good. I don't have the 302 GB that Apple claims, but I'm still good.

Apple recommends that I store all my documents in iCloud. But I have optimization disabled on this computer specifically so I have a local copy of iCloud data.

Apple tells me I can save space by automatically removing movies and TV shows that I'm already watched. I don't have any movies or TV shows.

Apple tells me I can save space by automatically emptying the trash. But right below that, Apple helpfully tells me that I have 113.9 MB in the trash. I don't think that's going to meaningfully impact storage on my 1 TB drive.

Apple does tell me that I have 11.61 GB of data in Apple Intelligence. But this is on Sequoia, where I still have a button to turn off Apple Intelligence. And it is definitely "off".

melvin3v wrote:

I have 170GB of System Data bloat with over 225GB of free disk space on macOS 27.0.1, so it just bloats regardless. And mine is brand new, only 10 days old. That only shows when my external SSD is plugged in. Immediately after ejecting it, System Data drops to 67GB.

That sounds like there is about 100 GB of stuff on the external that Spotlight hasn’t indexed or can’t identify.

Apple engineers advised me that macOS is creating one snapshot in case my external APFS drive becomes corrupt or isn’t ejected properly. They ran full diagnostics, and that’s what they reported back to me.

Sounds plausible.

So according to them, it’s completely normal, but IMO, it’s ridiculous. They could easily fix this, or maybe they just aren’t smart enough to properly label everything and be transparent. Who knows? 😂

There are lots of things that are not one of the listed categories, possibly because very few people care what they are.

It’s annoying, and yes, it’s purgeable space, but you shouldn’t have to buy a brand-new computer only to have macOS automatically take up a huge chunk of your storage and then basically say, “Well, you can have it back once your hard drive starts running out of space.”

If it goes away when you eject the drive, is it really taking up a “chunk of space?” An SSD cannot instantly reset the storage to make it useable immediately. If it magically disappears, it isn’t being taken away from you.

If it is a snapshot per Apple support, it likely is reporting the storage required if the snapshot was fully materialized on disk, not what it is actually used on disk.

Just my opinion. You’re ok with that, right?

Just to clarify, I actually have my external SSD specifically excluded from Spotlight indexing under the Spotlight Search Privacy settings, so Spotlight isn’t indexing that drive at all.

As for your explanation about macOS possibly reporting how much space a snapshot would require if it were fully stored rather than how much physical space it’s actually consuming, that does sound plausible. It could explain why the System Data figure changes so dramatically when I connect or eject the drive.

I actually asked the Apple engineers specifically why this happens almost instantly on my Mac. The engineer explained that on an older or slower Mac, or one with significantly more data on it, this process could happen gradually over the course of 3 to 5 days, so people might not even notice it happening. However, because my Mac is brand new, has very little data on it, and has extremely fast hardware, he said the process happens almost instantly.

Apple engineering ran full diagnostics and specifically reported back that macOS is creating a snapshot associated with my external APFS drive. That’s the explanation they gave me after investigating the issue.

I understand your point about the difference between reported storage and actual physical space being consumed, and I think it’s a reasonable possibility. I’m not claiming that 100GB is necessarily being permanently taken away from me.

My biggest frustration is that macOS reports roughly 170GB of System Data on a brand-new computer, then drops to around 67GB immediately after ejecting the external SSD, without clearly explaining what that additional 100GB actually represents. Whether it’s physically consuming that space or simply reporting the potential size of a snapshot, Apple should be much more transparent about it.

If the space isn’t actually being used, why display it in a way that makes it appear as though it is? That’s really my point. 😂

melvin3v wrote:

Just to clarify, I actually have my external SSD specifically excluded from Spotlight indexing under the Spotlight Search Privacy settings, so Spotlight isn’t indexing that drive at all.

That’s the whole point. If it cannot use Spotlight to determine what it is, it is all System Data.

If the space isn’t actually being used, why display it in a way that makes it appear as though it is? That’s really my point. 😂

The space is being used,

…on your external drive.

I always advise to never use the dynamically generated storage displays because they are infinitely confusing and mostly useless.

melvin3v wrote:

In my case, CleanMyMac...

Probably unwise. Long-time members here often refer to that piece of crapware as BrickMyMac, based on the number of problems it causes, especially after macOS updates.

melvin3v wrote:

In my case, CleanMyMac

Perhaps we're getting closer to the answer now.

I'm not one to disparage CleanMyMac that way other people do here in the forums. From what I see, it causes relatively few problems compared to how ubiquitous it is. But it most definitely is a "clean up" app. Technically speaking, you aren't having a problem. You're just poking around a little too deeply. CleanMyMac could be the cause of this strange behaviour with its "clean up" activities. All those "caches" and "junk" that it deletes will immediately become "System Data" until the system deletes it. And then, the system gets right back to work rebuilding all of it, which CleanMyMac will later dutifully delete again. Lather, rinse, repeat.

DaisyDisk were unable to locate the hidden System Data.

To get back to my previous point, that's like hiring an expert nature guide and asking him to guide you to Mirkwood forest. He can't find Mirkwood forest because it doesn't actually exist.

There are other forests you could explore, and many of them may have some very interesting flora and fauna. But if you want to explore, you have to stay grounded in the real world, not the make-believe one.

I migrated from an M1 MacBook Air with only a 256GB SSD annd 109gb free and there’s hardly anything on either computer. My Mac mini has a 512GB SSD with about 225GB free, yet System Data jumps to around 165GB whenever my external SSD is plugged in. As soon as I unplug it and reopen Storage settings, System Data drops back down to around 60GB.

I want to reiterate an important point here. Storage problems, especially "System Data" problems are one of the most commonly reported problems with macOS over the past several years. It's a major, major problem.

But in that all that time, you are the one person to report this specific behaviour. No one else - not even once.

Apple engineers told me this is normal behavior, which is frustrating. They were pretty firm in their explanation that macOS 27 creates a hidden snapshot in case the external SSD becomes corrupted or is improperly ejected. Whether that’s BS or not, I have no idea, but they spent a 3 days investigating before getting back to me with that explanation or that’s at least when supervisors responded 👍 And this is Os27 for me OP is on Tahoe I beleive.

A local snapshot isn't going to consume 100 GB. It's simply not possible.

melvin3v wrote:

In my case, CleanMyMac ... System Data jumps to around 165GB whenever my external SSD is plugged in. As soon as I unplug it and reopen Storage settings, System Data drops back down to around 60GB.

As @etresoft points out, that's not supposed to happen. Period. If that's what you see on your Mac, then there is something very odd with your Mac. I would guess that BrickMyMac is part of the problem, for sure it's not part of the solution.

You state that plugging in an external SSD makes your System Data jump by over 100 GB. As a benchmark, on Golden Gate 27.0.1, my System Data has been between 150-160 GB. I use many external SSDs, and I have never seen System Data change when mounting or ejecting any of them. So I decided to mount more than one.

Top to bottom on the right of System Settings, that's my 2 TB internal drive, a small locally-saved disk image, five external SSDs (a mix of Samsung T7 and T9 1 TB and 2 TB drives), and for good measure an SD card in the MBP's internal slot (shows as an SD card icon) and another SD card in the slot on my Thunderbolt dock. With all of those drives/cards mounted, System Data is showing as 152.76 GB.

I then quit System Settings, ejected all the mounted drives (and unplugged/removed the 7 external ones), re-launched System Settings and clicked on Storage, and waited a few seconds for System Data to finish calculating.

No change. Well, technically it went from 152.76 GB to 152.77 GB. It's definitely not >100 GB smaller after ejecting all the external storage media.

Interesting that you didn’t get the same result across seven SSDs. Since we’re on the same macOS version, are you also using an M6? I’m curious whether the hardware could make a difference, although I don’t know that it does.

Apple ran complete diagnostics on mine and said everything is running great. The engineer described my storage behavior as normal and said it involves a hidden mechanism to protect against disk corruption that isn’t listed under APFS snapshots. Disk Utility shows the space as purgeable on my Mac.

The supervisor said the reported usage may drop gradually over several days to a week, depending on how much data is on the drive. Someone I spoke with on Reddit reported similar behavior to mine, although theirs dropped by about 40 GB. I’d be interested to compare more reports from M6 users.

neuroanatomist wrote:

melvin3v wrote:

In my case, CleanMyMac ... System Data jumps to around 165GB whenever my external SSD is plugged in. As soon as I unplug it and reopen Storage settings, System Data drops back down to around 60GB.

As @etresoft points out, that's not supposed to happen. Period. If that's what you see on your Mac, then there is something very odd with your Mac. I would guess that BrickMyMac is part of the problem, for sure it's not part of the solution.

You state that plugging in an external SSD makes your System Data jump by over 100 GB. As a benchmark, on Golden Gate 27.0.1, my System Data has been between 150-160 GB. I use many external SSDs, and I have never seen System Data change when mounting or ejecting any of them. So I decided to mount more than one.

https://discussions.apple.com/content/attachment/659a1289-03e2-4924-be1a-706c767612e2

Top to bottom on the right of System Settings, that's my 2 TB internal drive, a small locally-saved disk image, five external SSDs (a mix of Samsung T7 and T9 1 TB and 2 TB drives), and for good measure an SD card in the MBP's internal slot (shows as an SD card icon) and another SD card in the slot on my Thunderbolt dock. With all of those drives/cards mounted, System Data is showing as 152.76 GB.

I then quit System Settings, ejected all the mounted drives (and unplugged/removed the 7 external ones), re-launched System Settings and clicked on Storage, and waited a few seconds for System Data to finish calculating.

https://discussions.apple.com/content/attachment/5e65633b-75ce-4373-aa87-9e3231dfe2bf

No change. Well, technically it went from 152.76 GB to 152.77 GB. It's definitely not >100 GB smaller after ejecting all the external storage media.

That's a great experiment and result, neuroanatomist. It shows that connecting and disconnecting external drives does not change System Data accounting by the Mac's Storage Tool. The user who was seeing this probably has installed things or made other configuration changes that have disrupted normal macOS operations. I agree with you that CleanMyMac is a prime suspect but I think other things could be installed as well.

My Mac is all good nothing corrupted Apple engineers just went thru and ran diagnostics and even had me send them clean my Mac screenshots 👍 If people do use clean my Mac just have to be smart and know what the heck your deleting and research. Where people get in trouble is if they go digging and delete files they shouldn’t have.

neuroanatomist wrote:

No change. Well, technically it went from 152.76 GB to 152.77 GB. It's definitely not >100 GB smaller after ejecting all the external storage media.

Good experiment. If it makes any difference, were the external volumes Spotlight-indexed?

BTW instead Time Machine, I use Carbon Copy Cloner which creates snapshots to the APFS backup volumes, if that makes any difference in this issue (with APFS, CCC "Safety Net" is not needed anymore). A few times I have mounted some old snapshot to grab some old document version, very handy.

And anyway, I have always ignored System Data.

External drive increased my system data and I have no other items that would cause this. I made no changes between OS26 and OS27. I show a difference of >10GB with my external TB5 drive on vs off.

steve626 wrote:

tbirdvet wrote:

External drive increased my system data and I have no other items that would cause this. I made no changes between OS26 and OS27. I show a difference of >10GB with my external TB5 drive on vs off.

Is that external drive also being backed up along with the internal drive, to a separate Time Machine drive? If so, there may be snapshots being generated from that external drive's contents and those snapshots might be included in the "System Data" accounting bin.

Or maybe all of the storage on your Mac is listed, and since it’s not being indexed, it’s all “System Data”. I pretty much doubt that, though, because I have several TB of attached storage and my System Data hovers around 60GB. I’ll have to see if I have any of it excluded. I’m pretty sure most of it is indexed, but I’ve backup drives (for the externals) that are excluded.

For those that see the drop, does it correspond to the data stored on the drive.

Barney-15E wrote:

steve626 wrote:

tbirdvet wrote:

External drive increased my system data and I have no other items that would cause this. I made no changes between OS26 and OS27. I show a difference of >10GB with my external TB5 drive on vs off.

Is that external drive also being backed up along with the internal drive, to a separate Time Machine drive? If so, there may be snapshots being generated from that external drive's contents and those snapshots might be included in the "System Data" accounting bin.

Or maybe all of the storage on your Mac is listed, and since it’s not being indexed, it’s all “System Data”. I pretty much doubt that, though, because I have several TB of attached storage and my System Data hovers around 60GB. I’ll have to see if I have any of it excluded. I’m pretty sure most of it is indexed, but I’ve backup drives (for the externals) that are excluded.

For those that see the drop, does it correspond to the data stored on the drive.

Barney-15E -- here's what I see on my MacBook Pro 16" Intel on Tahoe 26.7.1:

This laptop has a 1 TB internal drive. I connected two external drives, a 1 TB and 2 TB drives. Neither are used for Time Machine (those are two additional drives that were not connected for this experiment). Both are indexed.

Two external drives connected (1 TB and 2 TB)

1 TB internal drive shows in Disk Utility

518 GB available

485 GB free

33 GB purgeable

Storage Tool System Data: 49 GB

No drives connected

1 TB internal drive shows in Disk Utility

517 GB available

484 GB free

33 GB purgeable

Storage Tool System Data: 49 GB

Same System Data with or without external drives connected. All drives are indexed. (I don't understand the 1 GB of disagreement between the two cases for "free space" but assume that is not pertinent.)

etresoft wrote:

This is like people arguing over whether the Game of Thrones characters are more accurately depicted in the TV show or the books.

About something no one here understands. That’s why we have the long ongoing dissertations.

This. Thanks for telling us buying a new Mac is not a solution. I have a 1TB hard drive on a 2021 MacBook pro. Most of my files are in iCloud. That's because I have about 800GB of work sitting there. I have gotten to the point of turning iCloud off to see what happens. I gained all of 62GB on my internal hard drive. This seems to happen with and without optimization. My user account has me at about 550GB, but when I examine individual files, I see maybe 50 GB. WHERE IS THE BLOAT? I can literally wake up and see files are consumed so the Macbook can't scan, work, etc. Or move files to an external. I've seen I am not alone. I purged iMazing for my phone backup to see if it was that. Nope. What is frustrating is I have flown out of state to do some WORK and can't do basic operations because my internal hard drive is full. I can't use my externals because my hard drive is too FULL. I will purge/move whatever to gain space. But no. This is so frustrating!!!!

My Disk Utility says I only have 10 MB purgeable, still in OS 26. My "System Data" is currently at 186 GB after deleting two small Time Machine snapshots. Remaining space 138 GB. This is workable for me for a while as I do some catching up, but when I install OS 27, I'll be prepared to get a new 1TB system shortly thereafter if need be. I can't change Apple's MO, but I better understand the situation I have to work with.

I use Time Machine on an external hard drive and learned not to turn iCloud optimization on or the Time Machine backup will only include placeholders of all the content stored on iCloud until it's called up for service. Not sure if something like this is affecting what you can do and can't do, depending which storage you're trying to access your files from.

etresoft wrote:

This is like people arguing over whether the Game of Thrones characters are more accurately depicted in the TV show or the books.

A lot of people post questions here about what their Mac's Storage Tool shows (System Data especially) and since Apple hasn't really documented it, folks here are trying to understand it. Maybe simply a lost cause, as you have advised before.

Random comment: I have noticed that on my iPhone and Apple Watch (Series 11), there is also "System Data" shown but it is a very tiny fraction of total usage.

By the way, I think the book depictions are probably more accurate than the TV show.

mhb wrote:

I use Time Machine on an external hard drive and learned not to turn iCloud optimization on or the Time Machine backup will only include placeholders of all the content stored on iCloud until it's called up for service. Not sure if something like this is affecting what you can do and can't do, depending which storage you're trying to access your files from.

Backups normally back up only files that are physical on your Mac. When you move those files to cloud storage, they are no longer physically on your Mac and are no longer backed up. This can be a trap when people think they have backups but those backups do not include cloud stored files, which can be accidentally deleted or damaged or corrupted and then there is no backup.

One exception to this is that Carbon Copy Cloner is a backup tool that can back up cloud stored files, if the user instructs it to. It does this by temporarily downloading each cloud stored file, backing it up, and then removing it from local storage. As you might imagine, this could take a lot of time and backup storage space.

steve626 wrote:

A lot of people post questions here about what their Mac's Storage Tool shows (System Data especially) and since Apple hasn't really documented it, folks here are trying to understand it.

Absolutely. Can't blame them. It's a fancy user interface displaying lots of important-looking numbers. Some guy on the internet keeps saying it's nonsense. But why would Apple do that? Doesn't make sense.

Random comment: I have noticed that on my iPhone and Apple Watch (Series 11), there is also "System Data" shown but it is a very tiny fraction of total usage.

Not random at all. Many aspects of iOS work great on iPhones, but not so well on the Mac.

By the way, I think the book depictions are probably more accurate than the TV show.

But we can all agree that both are a poor attempt to copy Tolkien's work. The books, I mean. Don't get me started on the movies.

Barney-15E wrote:

That is interesting, but I thought mhb was still on Tahoe.

👍

Thanks, this is very helpful.

Matti Haveri wrote:

Good experiment. If it makes any difference, were the external volumes Spotlight-indexed?

All the external volumes are excluded from Spotlight indexing.

This is like people arguing over whether the Game of Thrones characters are more accurately depicted in the TV show or the books.

I have the same issue, basically my MacBook Pro is now unusable....

Wait and see what happens with the next macOS Golden Gate update and see what happens.

Thanks! I haven't used that app in ages and don't need it, so I cleared the cache file and deleted it :)