What is Time Machine Backing Up?

April 23, 2011 11:47 AM

Why is Time Machine backing up nearly a Gigabyte every time?

I have an external Hard Drive which I use to backup my MacBook Pro. Every single time it backs up it has to copy just shy of a gigbyte of files. I have no idea what is causing this as I have all of the regularly changing folders exempted from the backup (eg, my Downloads folder, Trash and Caches). What on earth is accumulating 900 Megs of change per hour? When I'm not doing anything other than browsing the web?

posted by dougrayrankin to computers & internet (11 answers total)

Do you have anything browser-related kept in a .dmg file or any other file containing a file-system? Touching anything within such a file will trigger a backup of the whole container. (Sparse-bundle .dmg can be backed up a little more efficiently but still by an amount larger than the contained file that was touched.)
posted by TruncatedTiller at 12:01 PM on April 23, 2011

Do you use a virtual machine to run Windows or Linux from within OS X? If so, make sure the machine image is excluded.
posted by caek at 12:06 PM on April 23, 2011

Are you using FileVault? This would cause a backup of your entire user folder as a unit, each time.
posted by birdsquared at 12:09 PM on April 23, 2011

No to all three, though if it helps I do dual boot with Windows 7, though this happens if I leave OSX running and do not boot into Windows.
posted by dougrayrankin at 12:32 PM on April 23, 2011

Are you running a local mail client like thunderbird?
Large mailbox files will update every time a new email arrives.
posted by Lanark at 1:35 PM on April 23, 2011

No to mail client either, I use hotmail... It's really perplexing.
posted by dougrayrankin at 1:37 PM on April 23, 2011 [1 favorite]

TimeTracker might show you what's changed between backups -- bottom of the page.
posted by Drama Penguin at 1:52 PM on April 23, 2011

I wrote a little command-line utility awhile ago to figure out what's changed in a Time Machine backup. It's not exactly built for user-friendliness though, sorry!
posted by vasi at 2:20 PM on April 23, 2011

I said TimeTracker might - but it will, I just tested out myself - works on the current version of snow leopard.
posted by Drama Penguin at 2:21 PM on April 23, 2011

It's probably a single binary file somewhere. Try searching for all files larger than 1 GB on your computer and look for ones that may be getting modified somehow.

You can do such a search by opening Finder, starting a search of any kind (just key in some letters in the top to kick it off), then click the plus sign just beneath the search bar. On the left of the bar pull down the menu and choose Other... then select Size from the giant list. Click OK. You're returned to the bar with Size selected. Choose Is Greater Than... 1 GB... and finally, take out the letters you typed earlier to start the search so that it catches any filenames.

Here's a screenshot of what you should have now.

Be sure you give it some time to finish the search.
posted by odinsdream at 7:06 PM on April 23, 2011

TimeTracker did the trick. It was a log file from mongodb, a part of an old diaspora installation I was playing with.
posted by dougrayrankin at 4:12 AM on April 24, 2011