Information Technology Reference
Manage Your Time Machine Schedule
Apple believes that most Time Machine users will back up either to
a local drive that's always connected, or to a network volume that's
always available. However, if you travel with a laptop, or if for any
other reason your destination disk isn't always available, don't worry:
Time Machine still works fine—with some qualifications.
Mac, Time Machine puts its regular hourly backup snapshots in a
hidden location on your startup disk even when your destination disk
is disconnected, and then transfers those locally stored snapshots to
your usual Time Machine disk once it becomes available.
However, if you don't have a Mac with local snapshots enabled,
whenever your backup disk isn't available, your files won't be backed
up at all—and the only notice Time Machine gives, for the first few
days, is a discreet change in its menu bar icon. (A similar icon
appears if a backup was not merely delayed due to unavailable media
but failed for some other reason.) So if you expect to spend long
periods of time during which your regular Time Machine destination
disk is unavailable, consider using a supplemental backup, such as
an Internet backup service or a portable hard drive.
Sometimes you may want Time Machine not to run, even though its
destination disk is connected. You may, for example, want to make
sure every last bit of your computer's CPU is available to devote to
some important task, or you may want to keep a noisy external drive
quiet for part of the day. Any time you want to suspend Time Machine
from running backups, open the Time Machine preference pane and
move the big switch from On to Off. Time Machine remembers all its
settings, and resumes backups whenever you turn it back on.
On the other hand, in some situations you may want to make sure
Time Machine immediately backs up your files. For example, you may
have recently saved or downloaded an important document, but the
next scheduled Time Machine run isn't for another 45 minutes. No
problem: you can force an immediate backup, even if Time Machine