AUGUST 2019 MACWORLD 115the volume isn’t formatted using the old
standby, HFS+, labeled “Mac OS Extended
(Journaled)” in Disk Utility.
Time Machine can only create backup
archives on HFS+ volumes because of
some of the peculiar properties of how it
creates snapshots by referencing files with
hard links. These links allow the same file
to appear as if it’s in multiple places on a
single volume, even though only a single
copy of it occupies space on the disk.
Despite Apple’s adoption of APFS,
Time Machine cannot use volumes from
drives in this format. It’s more likely that
you have a disk formatted at some point
for a Windows or Unix system, likely using
MS-DOS FAT or ExFAT formats.
If you want to use a disk in one of
those formats, first back up any data you
need to preserve from the disk: there’s
no way to reformat without erasing the
drive’s contents. Next, follow Apple’s
instructions to erase and reformat it as a
Mac OS Extended volume (go.macworld.
com/erse).WHEN THE VOLUME MOUNTS
AGAIN, TIME MACHINE WILL
RECOGNIZE IT AS A
DESTINATION
What to do if your Mac’s hard drive starts
unmounting itself unexpectedly
When you mount a drive in the Finder,
you expect it to stay there. If you’ve found