Time Machine - Troubleshooting

D3.  TM is doing a full backup for no good reason

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Time Machine will always do a full backup in these circumstances:

  1. Backing-up from a new disk or partition (only that disk/partition gets a full backup).

  2. Backing-up to a new or erased disk or partition.

  3. After a full restore (not a "smart update") from a "clone" such as CarbonCopyCloner or SuperDuper.  This includes getting a new HD or erasing your current one, and using the clone to restore your data.  Effective with Lion 10.7.x, you may be able to prevent it via item #B6).

  4. After replacing or erasing your internal HD, and putting your data back “piecemeal.”  This includes dragging selected items or restoring selected items via the Time Machine “Star Wars” display.  Effective with Lion 10.7.x, you may be able to prevent it via item #B6).

  5. Going many days (at least 10, usually many more) without a backup, if a lot of changes have been made.

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In other situations, there are some differences depending on the version of OSX your Mac is running.  (If you're not sure what version you have, click here).

Mountain Lion and Lion (10.8.x and 10.7.x):

  1. A new or erased internal hard drive if restored via Time Machine full restore, Setup Assistant, or Migration Assistant, Time Machine should not do a full backup.  It should take quite a while to prepare, but only back up what’s changed.  But if it does start a full backup, you may be able to prevent it via item #B6).

  2. Getting a new logic board (motherboard) in your Mac: Time Machine should not do a full backup.  It should take quite a while to prepare, but only back up what’s changed.  If it does start a full backup, you may be able to prevent it via item #B6).

  3. If you get a new Mac, see item #B5.


Snow Leopard (10.6.x):

  1. A new or erased internal hard drive if restored via Time Machine full restore, Setup Assistant, or Migration Assistant should not do a full backup.  It should take quite a while to prepare, but only back up what’s changed.  Sometimes, however, Time Machine does a full backup.  If it does, there’s no way to prevent it.

  2. Getting a new logic board (motherboard) in your Mac: Time Machine should not do a full backup.  It should take quite a while to prepare, but only back up what’s changed. Sometimes, however, Time Machine does a full backup.  If it does, there’s no way to prevent it.

  3. If you get a new Mac, see item #B5.


Leopard (10.5.x):

  1. A new or erased internal hard drive if restored via Time Machine full restore, Setup Assistant, or Migration Assistant will do a full backup. There’s no way to prevent it.

  2. If your Mac's logic board (motherboard) is replaced, Time Machine will do a full backup.  There is a possible, but rather difficult, workaround.  See item #C8.

On occasion, a corrupted preferences file may cause repeated full backups.  Try a "full reset" of Time Machine, per item #A4.

If nothing here helps, see item #D7.