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Time Machine backing up entire drive each time.

I use a 500 GB FireWire drive to share files between my two computers (iMac and MacBook Pro) in order to get better performance out of programs like Logic, and not have to worry about syncing my files. Obviously, due to the portable nature of all my data, it is IMPERATIVE that I have a backup.

I have a 2TB Lacie drive plugged into my imac which backs up the iMac and the External dive when it's available, the MacBook Pro is setup such that it backs up to the same drive over the network when it is available. The MBP does NOT backup the external drive when it's connected, it only backs up from the imac. I have several other drives daisy chained on the imac of crap files that don't matter, and they don't back up at all (the external is added to the end of this chain, and the Time machine disk is first, though I can't imagine how this could have any effect.)

Anyways, every time I work on the MBP and then re-plug the drive into the iMac to continue work and do a backup, the time machine starts from scratch and backs up the entire drive.

I thought that my backup may have been corrupt, so I wiped the time machine disk and started fresh, but it's still doing it. This was not happening a few months ago, so I'm not sure what's changed.

Any thoughts?

iMac, Mac OS X (10.7.2), 27", 2.66 i5, 16 GB RAM, 1TB HDD

Posted on May 4, 2012 1:12 PM

18 replies

Linc Davis

Level 10

209,547 points

May 4, 2012 7:53 PM in response to ChickenMuffin

I've never done what you're doing, so I don't know. If you want to try an experiment, proceed as follows.

After backing up the drive, connect it to the other host, but don't change any fiies. Then reconnect it to the host that does the backups. Turn TM off temporarily.

Launch the Terminal application in any of the following ways:

☞ Enter the first few letters of its name into a Spotlight search. Select it in the results (it should be at the top.)

☞ In the Finder, select Go ▹ Utilities from the menu bar, or press the key combination shift-command-U. The application is in the folder that opens.

☞ Open LaunchPad. Click Utilities, then Terminal in the page that opens.

Drag or copy — do not type — the following line into the Terminal window, then press return:

sudo tmutil compare

You'll be prompted for your login password, which won't be displayed when you type it. You may get a one-time warning not to screw up.

The command will take at least a few minutes to run. Eventually some lines of output will appear below what you entered.

Each line that begins with a plus sign (“+”) represents a file that has been added to the source volume since the last snapshot was taken. These files have not been backed up yet.

Each line that begins with an exclamation point (“!”) represents a file that has changed on the source volume. These files have been backed up, but not in their present state.

Each line that begins with a minus sign (“-“) represents a file that has been removed from the source volume.

Files that you’ve excluded from backup, or that are excluded automatically, are ignored.

At the end of the output, you’ll get some lines like the following:

-------------------------------------

Added:

Removed:

Changed:

These lines show the total amount of data added, removed, or changed on the source(s) since the last snapshot.

May 6, 2012 6:21 PM in response to Linc Davis

Hey Linc.

Sorry, I appreciate your input but haven't had a chance to try your solution yet. I'll get back to you tomorrow when I get a chance to try it out.

emanres

Level 1

4 points

Jun 18, 2012 3:21 PM in response to ChickenMuffin

Hey ChickenMuffin,

I don't know if you've solved your problem yet, but I may have a possible solution.

I was having the same problem as you, albeit on Snow Leopard. It was backing up a full 200GB, which I knew couldn't be right. And then I noticed something--the drive hadn't turned blue like it used to (it was still a regular yellow). So I went into Time Machine preferences while it was updating, clicked "Select Disk...", and chose the drive I was using. It turned blue and automatically cancelled the previous sync and started a new one.

As you suggested, this problem probably is due to using the same hard drive on two computers. Previous to this update, I used this hard drive to transfer some big files to another computer.

I know this seems really simple compared to some other answers on this thread, but I hadn't seen anyone post it yet. Hopefully this helps you, and anybody else.

Regards,

emanresu

Time Machine backing up entire drive each time.