Why is Time Machine trying to backup so much?

November 29, 2012 4:46 PM

Why is Time Machine trying to backup 35 GB of data every single day when I'm only using 300 GB of my 500 GB HD and I know I have not changed or added that much in the time since my last backup?

I have a MBP running 10.6.8 that I am backing up and a Mac Mini running Mountain Lion (and Server) hooked up to a 2 TB external drive that acts as my NAS and Time Machine. The Mac Mini is connected to my wifi router via ethernet and acts as my home server. Using Mountain Lion Server, I've set it up as a Time Machine server as well.

Every time I come home and connect to the wifi network it does it's daily backup as expected, but it is so much bigger than expected. I was under the impression the backups were only supposed to copy new files or altered files, and there is no way I'm changing 10% of my drive each day at work...

posted by pwb503 to computers & internet (12 answers total)

Do you have a large file like a virtual machine through VMWare Fusion or Parallels?
posted by drpynchon at 4:49 PM on November 29, 2012

You can use the app TimeTracker (Scroll down on that page, there's no anchor link for the utility) to see exactly what's in any particular Time Machine backup.

I had a similar problem on a smaller scale (4-6 gigabytes per backup when I was expecting maybe a few megabytes) and TimeTracker caused me to notice that Thunderbird's "one file per mailbox" style of mail storage was the cause. I changed the way I archived my work email and that fixed the issue.
posted by bcwinters at 4:52 PM on November 29, 2012 [2 favorites]

There are some simple things that can throw Time Machine, like the clocks being off, or go ahead and one night connect the MBP via ethernet and let it get some big change over it cannot handle otherwise if one or the other machine is going to sleep.

If you open up the console utility from the Utilities folder, scanning through the logs can get you some Time Machine errors, and googling those may point you to the real problem.
posted by nickggully at 4:52 PM on November 29, 2012

I do have a parallels VM. I don't know how big it is offhand. That might be it though I guess. Any other ideas?
posted by pwb503 at 5:02 PM on November 29, 2012

It is parallels.

Start the VM up, go to Virtual Machine -> Configure -> Options -> Back up and select the box Time Machine: Do not back up virtual machine
posted by dfriedman at 5:05 PM on November 29, 2012

Search for ".pvm" on your computer in Spotlight. Parallel's VM files have this extension. Then you can get details on the file including its size. This is a common issue with incremental file backups (regularly updated large files like VMs or encrypted folders). The simplest solution (at least in Fusion) is to keep your VM's data files in a Virtual Folder accessible by the primary OS, and exclude the VM file itself from backups. Of course, if you are running the VM as a sandbox for security reasons, this might be a problem.
posted by drpynchon at 5:10 PM on November 29, 2012

Probably not the cause of an entire 35G, but you could also be playing music from this machine constantly, which could be updating metadata like playcounts and causing the files to be backed up.
posted by jacalata at 5:16 PM on November 29, 2012

Things that I've found lead to bloated Time Machine backups:
* Thunderbird, and other mail clients that use MBOX (one file per mail folder)
* Google Chrome: The cache and history are made up of large files that seem to get updated frequently.
* Virtual Machines.
posted by Good Brain at 6:13 PM on November 29, 2012

Probably not the cause of an entire 35G, but you could also be playing music from this machine constantly, which could be updating metadata like playcounts and causing the files to be backed up

iTunes does not store play count in the music files themselves. This should not cause Time Machine to back up your music constantly.

There are some simple things that can throw Time Machine, like the clocks being off

If the system clock is obviously incorrect (logically too far in the past), Time Machine should detect this and display an error dialog. Otherwise, some clock drift shouldn't have an effect.

In OS X Lion or later, /usr/bin/tmutil can help you figure out what's changing between snapshots (among other things). It won't run on Snow Leopard, but your Mountain Lion machine can use it to analyze the Snow Leopard backup.

Example:

cortana:~ mikey$ cd "/Volumes/Time Machine Backups/Backups.backupdb/cortana"

cortana:cortana mikey$ ls -l
total 8
drwxr-xr-x@ 3 root  wheel  238 Nov  9 16:20 2012-11-09-162004
drwxr-xr-x@ 3 root  wheel  272 Nov 13 15:11 2012-11-13-151149
[snip snapshots]
drwxr-xr-x@ 4 root  wheel  340 Nov 29 18:12 2012-11-29-181233
drwxr-xr-x@ 4 root  wheel  340 Nov 29 19:12 2012-11-29-191200
lrwxrwxrwx  1 root  wheel   17 Nov 29 19:12 Latest -> 2012-11-29-191200

cortana:cortana mikey$ sudo tmutil compare 2012-11-29-181233 2012-11-29-191200

[snip detailed comparison output]

-------------------------------------
Added:         8.5M
Removed:       352.8K
Changed:       11.9M

Run `man tmutil` for information about comparing backups using tmutil.
posted by Mikey-San at 7:26 PM on November 29, 2012

I know that VMware Fusion has a TimeMachine friendly system for storing VMs now. Basically it's constantly taking snapshots of the VM. That way the vast bulk of the VM drive hasn't changed, and TimeMachine only needs to copy over the new snapshot.

Looks like Parallels has a similar option. You'll want to turn this on if you still want your VMs in TimeMachine.
posted by sbutler at 8:23 PM on November 29, 2012

An update to the OS just came out that affects the way Time Machine backs up -- when's the last time you updated? I suggest this only as a partial solution/answer, but it couldn't hurt to check. The description on Software Update said it makes changes to speed up TM backups (which was the problem I was having...it's been 2 weeks of continual backup and my new 3TB drive still hasn't fully completed its first backup), so we'll see if it affects it in any other way, too.
posted by bitter-girl.com at 5:50 AM on November 30, 2012

Thanks for all your help. I have been using Parallels almost daily for the last week or so which is why this started happening. Removing it from the backup fixed the issue.
posted by pwb503 at 12:03 PM on December 3, 2012