User level: Level 1 (26 points)Trying to set up external drive for time machine. Disk Utility (after setup) is refusing my 2TB drive and telling me I need a 5 TB drive. For a 512 MacBook?!?
Help appreciated!
Posted on Oct 13, 2026 11:45 AM
User level: Level 9 (72,871 points)Oct 13, 2026 1:38 PM in response to chuck3400
It’s recommended to back up to an external drive that is 2-3x the size of your internal storage.
Back up your Mac with Time Machine - Apple Support
With any new external drive (SSD/HDD, not applicable to NAS drives), the first time you connect the drive use Disk Utility to completely erase it, format it as GUID/APFS and apply encryption if desired. In Disk Utility, select View menu > Show all devices, then select the top level of the external drive and click Erase.
First set the Scheme to GUID then set the Format to APFS or APFS (Encrypted), only select a case-sensitive option if you know that you need that and why.
More info: Disk Utility User Guide for Mac - Apple Support
When the disk will be used for Time Machine, it's better to skip encryption at this step and select the encryption option when setting up the Time Machine backup.
Lacie/Seagate, Samsung, SanDisk, etc., all provide 'drive management' software on their drives and using such 3rd party software can cause issues when macOS is updated and the 3rd party software becomes incompatible. Even if there is no additional software on the drive, it will probably not have the correct format for optima use with a Mac. For example, Crucial SSDs come blank but formatted as ExFAT (a format for both Windows and Mac but not optimal for Mac, and not usable for a Time Machine backup, which requires APFS).
User level: Level 10 (242,520 points)Oct 13, 2026 12:03 PM in response to chuck3400
Disk Utility has no Time Machine drive detection or set up for it directly, so not entirely sure what you are seeing.
Can you post a screenshot? Redact any personal info.
To set up an external drive for TM backups, you do so from the Time Machine app directly, not Disk Utility.
To set up a drive for Time Machine, plug it in, open the Time Machine app and follow on-screen prompts when asked if you want to set up the drive for Time Machine backups.
It should not require any specific size of drive. Though at least double your hard drive size is recommended, so a 2TB drive should be fine for a 512GB internal drive.
click here ➜ Back up your Mac with Time Machine - Apple Support
User level: Level 1 (26 points)Oct 13, 2026 2:51 PM in response to neuroanatomist
Got it sorted. Thanks for the help!
User level: Level 1 (26 points)Oct 13, 2026 2:51 PM in response to chuck3400
Got it sorted. Thanks for the help!
Originally posted at discussions.apple.com/thread/256375632