Information Technology Reference
2. In the dialog that appears, click the plus button, navigate
to the item you want to exclude, select it, and click Exclude. (To
find files that are normally invisible, check Show Invisible Items.)
Alternatively, you can drag any item (a file, folder, or volume) from
your disk into the Exclude These Items from Backups list. When
you're finished, click Done.
(Unfortunately, Time Machine offers no way to exclude files that
meet certain criteria, regardless of their location—for example, all
files over 2 GB or all disk images. The only way to automatically
exclude a set of files whose members may change over time is to
exclude the folder that contains them. However, see the tip below
about using smart folders, just after these steps.)
3. If the item has already been backed up and you want to remove
it from Time Machine's backup on your backup disk (for example,
because it's large and you want the disk space for other files), follow
4. If you had previously turned Time Machine off, click On now.
Using Smart Folders for Exclusions
Having trouble locating files you want to exclude? Using the Finder's
Smart Folder feature, you can create a saved search for files that
meet certain criteria (such as “size is greater than 2 GB”). In Time
Machine's Options window, you can then locate that smart folder
and select its contents (hold down the Shift key to select multiple
files at once) to add them to the Exclude These Items from Backups
list. Do not simply add the smart folder itself, because that excludes
only the file representing the saved search rather than the files that
match the search. From time to time, repeat this procedure, as the
smart folder's contents may change.
Tip: If you exclude an item from Time Machine in this way and then
move that item in the Finder, Time Machine won't realize it's the
same item and will start backing it up! But there's a way to make
exclusions “sticky” so they follow items even if you relocate them. For
details, see Kirk McElhearn's explanation at Mac OS X Hints .