Time Machine problem: backup disk ran out of space unexpectedly

Question

Hi all,
I'm having trouble with Time Machine.  Each time it tries to do a backup, it errors out.
Here is the most recent log from TM Buddy:
Starting manual backup
Backing up to: /Volumes/Time Machine Backup/Backups.backupdb
Using file event preflight for Macintosh HD
Will copy (740.5 MB) from Macintosh HD
Found 1702 files (741 MB) needing backup
2.43 GB required (including padding), 57.43 GB available
Stopping backup.
Error: (-34) SrcErr:NO Copying /Users/Alan/Pictures/iPhoto Library (original)/Masters/2013/02/25/20130225-174952/IMG_1601.MOV to /Volumes/Time Machine Backup/Backups.backupdb/Alan’s iMac/2013-07-27-024450.inProgress/FE0FAB85-8482-43AF-B2D2-CB4804D0B0E9/Macintos h HD/Users/Alan/Pictures/iPhoto Library (original)/Masters/2013/02/25/20130225-174952
Copied 111323 files (57.29 GB) from volume Macintosh HD.
Copy stage failed with error:28
Backup failed with error: 28
It usually errors out in the middle of trying to backup the very large "iPhoto Library (original)" file, so I went digging into this file back in time.  About a month ago, I emptied the trash in iPhoto for the first time, and the size of the iPhoto Library file shrank from 87 GB down to just 1 GB.  That seems rather extreme, and according to iPhoto, I still should have approximately 62 GB of photos remaining.  The last completed backup that Time Machine was able to make had the library file at 800 MB.  Even more strange, the current iPhoto Library file on my iMac is 83 GB.  So I think this is the reason why TM is trying to make another complete backup of this file.
I'm guessing that if TM is able to completely backup the iPhoto Library file, the errors will go away.  Does this seem like a reasonable hypothesis?
If so, then I'll need to delete files on the TM volume to make more room.  At one point last year, I had tried splitting my monolithic iPhoto Library into 3 smaller libraries, and later merged them again under the current name "iPhoto Library (original)".  These changes/instances of the libraries were all captured on TM.  If I delete the original monolithic iPhoto Library file (named "iPhoto Library") on the TM volume, will I also lose my current iPhoto library (named "iPhoto Library (original)"?  In other words, how does TM distinguish one file from another?  By the file name?  Or some other more permanent identifier?

Answer 1

The backup volume was full. That shouldn't happen, because TM is supposed to manage disk space by deleting snapshots as needed to make room for a new one, up to the last complete snapshot, which is never removed automatically. Normally, a snapshot won't be started if there isn't enough space for it.
First, I strongly suggest that you make a new backup (not necessarily with Time Machine) on another external drive. A single backup isn't enough to be safe.
One possibility is that you were writing other data to the volume during the backup. Apple recommends that no other data be stored on a backup volume.
If you've moved any files to the Trash on the backup volume, empty the Trash.
Sometimes a reboot will clear the error.
Otherwise, turn Time Machine OFF temporarily in its preference pane. Launch Disk Utility, select the backup volume, and run Repair Disk. That operation may take a few hours. If the volume is repaired successfully, or if no problems are found, try another backup.
If TM still isn't working right, boot into Recovery (command-R at startup) and repair the startup volume ("Macintosh HD," unless you gave it a different name.) Reboot as usual and try TM again.
As a last resort, put the backup drive aside and don't use it until you're sure you'll no longer need the data. Then erase it and start over. Do this only if you have at least one other backup device.