146 MACWORLD AUGUST 2021
HELPDESK MAC 911Ask Mac 911
We’ve compiled a list of the most commonly
asked questions we get, and the answers
to them: go.macworld.com/mac911faq to
see if you’re covered. If not, we’re always
looking for new problems to solve! Email us
at [email protected] including screen
captures as appropriate.
Mac 911 can’t provide direct email re spons es
or answers for every question and we don’t
provide direct troubleshooting advice. For that,
turn to AppleCare, an Apple Store Gen ius Bar,
or the Apple Support Communities.The units of measure on an APFS-
formatted drive are containers, which are
collections of volumes. In HFS+, drives
were partitioned solely into volumes. One
way to think about it: HFS+ was a carton of
eggs, each egg a volume. APFS is a box
that contains cartons of eggs.
Each APFS container has a fixed
portion of the drive’s storage space
allocated to it (as in partitioning) or can fill
the entire drive. But volumes within a
container share the container’s allocation
dynamically. In most cases, adding
volumes to an existing container makes
more sense than adding containers,
because volumes can grow or shrink
without any work on your part. This allows
the greatest flexibility.
However, a disk used for Time Machine
backups is quite particular. As explained in
the column referenced above, Big Sur
adds a new “role,” or volume type, called
“Backup.” But, as Apple additionally notes
in the Big Sur manual (fave.co/3hwDufY),
that Time Machine volume requires the
entire disk. That’s a little confusing, isn’t it?
(A few readers have written in wondering
what it means, in fact.)
What Apple appears to be saying is an
APFS Time Machine volume requires a
single container that takes up the entire
disk—you can’t add other containers, and
that container has access to all the storage
space on the disk. Within that container
lives a Time Machine volume. If you want
to use the disk for other purposes, don’t
add a container; instead, use Apple’s
advice and add a volume within the
existing container (fave.co/3woWouQ).
That is limiting, because the Time
Machine backup could eventually swell to
fill the entire available storage in the
container (and disk), crowding out the
other volume or volumes you create.
However, Time Machine automatically
purges older files and attempts to keep
itself to a reasonable size, while still
offering significant points to revert to. You
can also delete older backup snapshots
and backed-up files following this advice
from Macworld UK (fave.co/3jJKcSp). ■