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Is it safe to manually delete files and folders from a time capsule? ( Apple's Time Machine backup system calls backup partitions that way )
Because using TM's option Delete all backups of ... is taking for ever >:(

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I wouldn't. I'd be patient and use 'Delete all backups'. –  user3463 Nov 25 '10 at 22:36
    
I'm tempted to say: yes, it's safe. But it makes me wonder what TM could be doing... If directories have not changed at all, TM creates a hard link to the existing (previous) backup of that directory. If a single file in a folder has changed, I guess it creates hard links for the non-changed files then, and only copies the changed file to that same backup folder? Removing all occurrences of a file would then leave you with hard links for each file in that folder, while maybe that could be optimized by creating a single hard link to the whole folder? But I doubt TM is optimizing things? –  Arjan Nov 25 '10 at 22:41
    
Are you removing a file or a folder? Or are both taking forever? And maybe TM is verifying the backup first? (See the log in Console.app for some clues about what TM is doing. Or see What is Time Machine doing? on Server Fault.) –  Arjan Nov 25 '10 at 22:45
    
Ok the process was taking like one hour, I went away 3 hours and now it's done, so it must have taken from 1 to 4 hours. I was deleting like 10 GB from the initial backup so maybe it made sense that it took so long, although deleting such big files shouldn't take that long, if it's just deleting, but obviously TM is doing something else which takes so long –  Petruza Nov 26 '10 at 1:45

2 Answers 2

up vote 1 down vote accepted

Yes, it is safe to manually delete backups. It won't be any quicker, though. Time Machine uses hard links to save space. A hard link is where a physical file on your hard disk is mapped to by multiple logical files (i.e. what you see in the Finder). When Time Machine is backing up, it hard links all files that haven't changed. This is how it can have multiple copies of them in the backup without them taking up any space - all the logical files are pointing to the same physical files on disk.

Using hard links, however, makes deletions take a long time. When you don't have any hard links, all you need to do to delete a file is remove the logical file from your directory structure, then erase the physical file on disk*. When hard links are in use, things are more difficult because you can't just delete the physical file straight away - another logical file might be mapped to it. You need to check that none remain, and this is time-consuming. You have to do this because if you didn't, and left the physical file untouched, it'd eventually be left 'orphaned' - using up space on the disk, despite not being referenced by any logical files.

This is why the delete takes so long (actually, the "preparing to delete" period - not the actual delete itself). Deleting with the Finder wouldn't be any quicker than deleting with Time Machine - both are constrained by the underlying file system.

*It's fairly common knowledge that file systems don't normally erase the actual data on disk when a file is deleted, so if you want to be pedantic, read "erase the physical file" as "mark the physical file's locations as free".

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Reformatting the drive should be the first option for most people, as manually deleting folders can take quite awhile & its pain in the rear. Also, the system may not delete files properly, and the trash does not empty completely. (Which is a minor problem)

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