To judge by a recent spate of email, Mac users are using Windows and Unix/Linux compatible drives more than ever. Many people have asked why their external drive appears and is grayed-out in the Time Machine preference pane’s excluded list. (Open the Time Machine preference pane and click Options to see that list.)
That’s because the drive isn’t formatted in a way that Time Machine can back up files from. While I’ve covered this in previous columns, it’s worth a quick refresher, given how many people are apparently currently dealing with this.
Time Machine volumes must be HFS+ formatted, listed in Disk Utility as “Mac OS Extended (Journaled)”.
Time Machine can only back up volumes formatted either as HFS+ or the newer APFS format.
While Macs can back up to a networked Time Machine destination, including a Time Capsule, all drives backed up still must be HFS+ or APFS formatted.
If you’re not sure how your drive is formatted:
Select the drive in the Finder. (If it doesn’t appear, select Finder > Preferences, click General, and check the External Disks box.)
Select File > Get Info.
Examine the Format field.
If the Format line reads anything but APFS or “Mac OS Extended (Journaled)”, Time Machine can’t handle it.
The solution is to make a copy through another means—Disk Utility or a cloning tool like SuperDuper! or Carbon Copy Cloner—and then erase the original drive, reformatting it with one of the types acceptable to Time Machine. Then restore your data back over.
However, if you need a formatted drive compatible with Windows or other platforms, you will need to skip Time Machine. You can use Arq or ChronoSync for incremental backups, the above cloning software for nightly updates to another drive, and/or an cloud-hosted backup service that archives external drives as well as your startup volume, like Backblaze.
This Mac 911 article is in response to a question submitted by Macworld reader Chris.
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Author: Glenn Fleishman, Senior Contributor
Glenn Fleishman’s most recent books include Take Control of iOS and iPadOS Privacy and Security, Take Control of Calendar and Reminders, and Take Control of Securing Your Mac. In his spare time, he writes about printing and type history. He’s a senior contributor to Macworld, where he writes Mac 911.