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I am reaching the capacity limit of my Time Machine drive.

Instead of purging snapshots from way back when, I'd like to just delete the backups of large files that I definitely do not need (such as the contents of the Downloads folder).

It seems that the "Delete all backups of selected files" would work here.

I am just a little worried that this could do such additional "magic" under the hood, rather than just deleting the old backups. For example: Prevent future versions of the file from being backed up, or causing the files to be also deleted from other Time Machine drives that I attach later.

Can someone confirm that none of this happens?

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up vote 7 down vote accepted

The "Delete all backups of selected files" will work for the old files, but I'm not sure it will do the magic you want. Time machine keeps only one copy of an unchanged file -- regardless of how many times you've run Time Machine.

I don't think deleting this will prevent future backups.

You should, however, exclude your Downloads folder and other piggy folders from the Time Machine backups. Go to Time Machine preferences and click the "Options..." button. Things I exclude from my backups include:

  • Downloads
  • Applications (I can download them again)
  • Certain big parts of developer tools such as WebKit frameworks
  • Google Desktop director (Google desktop can rebuild its index)
  • Dropbox folder (I'll let manage that backup)
  • Movies folder (mostly things I've bought from iTunes store, I can download again)
  • Previous systems (I've already copied these to an external disk separately)
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> 'but I'm not sure it will do the magic you want.' That is fine, I wanted it to NOT do any magic. – Thilo Aug 11 '09 at 0:51
As for excluding stuff from the backup, I do not want to do that, at least not for all TimeMachine volumes. I have an "online" backup disk that is always connected (and has still enough disk space), and an "off-site" disk that I connect every two weeks to take a snapshot. The "off-site" disk is almost full, so I want to put only really important stuff on there, but still keep everything and the kitchen sink on the "online" disk. – Thilo Aug 11 '09 at 0:54
For Dropbox, you may also need to exclude ~/.dropbox/cache or maybe even the whole folder? – Arjan Aug 12 '09 at 15:13
Interesting, I wasn't aware of ~/.dropbox. Currently my ~/Dropbox is 2.2M but ~/.dropbox is 28K – Doug Harris Aug 13 '09 at 14:54
I did exclude Applications, but when my laptop HD crashed it was painful finding the disks for Office suites/ iLife etc, remembering what to download etc. was a real pain. I don't exclude this folder any more - it's not like it changes much. – alimack Oct 18 '10 at 8:28

If you're using a sparse bundle then you may have much more space available than you think. But: you might want to manually reclaim that before Time Machine deletes old backups. See some details at the part about "If you are using a sparse bundle (like when using a backup on the network)" in What is Time Machine doing? on Server Fault.

(When you delete all backups of a file, then I assume a new backup is created when you change the original, or maybe even when some other file in that folder changes. Because Time Machine is triggered by changes on folder level, I guess it may find that some file is not on the backup disk when it processes that folder due to some other change in that same folder. But that's easily tested with a dummy text file, right?)

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Some more good stuff to exclude that I found using GrandPerspective:

  • ~/.dropbox (if you don't exclude your whole dropbox)
  • Your Downloads folder (mine's in dropbox anyway)
  • Folders where importers put things that you move every time, e.g. Easy VHS to DVD conversions, imports of movies from my Flip video camera, etc.
  • Music/Podcasts (these eat up a lot of space and for most I can get back-episodes if I need, plus I never want to :P)
  • ~/Library/Application Support/SyncServices omg this changes everytime you sync. I had a gajillion copies on my Time Machine drive
  • /Library/Updates the OS likes to keep copies of the packages from automatic updates. Why? who knows but you don't need 'em
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