Information Technology Reference
In the Time Machine preference pane, the master switch automatically
moves from Off to On, and a timer begins a 2-minute countdown
before your first backup begins. (You may prefer to turn it off until
you've excluded files from Time Machine, which I talk about next.)
During each of Time Machine's hourly runs, it backs up only the files
that have changed since its previous run (except files you've excluded,
as I discuss next). If an application stores its data as a package (that
is, a folder that looks like a file in the Finder), Time Machine backs up
only changed items within the package. (Among many others, iPhoto,
GarageBand, and DEVONthink use packages for their data.) However,
be aware that Time Machine won't back up iPhoto or Aperture while
the application is running.
Note: If you're using a Drobo device as a destination, read Drobo's
support article How do I make Time Machine work with Drobo? for
Exclude Files from Time Machine
By default, Time Machine backs up all the files on your hard disk
or SSD as well as any other locally connected volumes. That's usually
exactly what you want. However, in a few situations you may want
to exclude certain items from being backed up.
One obvious reason is a lack of space: if you have too much data
on your main disk(s) to fit comfortably on your backup destination,
something has to go. Out of concern for privacy or security, you may
prefer to leave certain sensitive files out of your backups. Another big
reason is performance: some files are so large and change so frequently
that they keep Time Machine busy doing virtually continuous backups.
Read Items to Consider Excluding , shortly ahead, for advice about
what Time Machine should not back up.
To make sure an item doesn't get backed up:
1. Open the Time Machine preference pane and click Options.