TIme Machine backup grows too large during backup process

Question

I have been using Time Machine without a problem for several months, backing up my imac - 500GB drive with 350g used. Recently TM failed because the backups had finally filled the external drive - 500GB USB. Since I did not need the older backups, I reformatted the external drive to start from scratch. Now TM tries to do an initial full backup but the size keeps growing as it is backing up, eventually becoming too large for the external drive and TM fails. It will report, say, 200G to back up, then it reaches that point and the "Backing up XXXGB of XXXGB" just keeps getting larger. I have tried excluding more than 100GB of files to get the backup set very small, but it still grows during the backup process. I have deleted plist and cache files as some discussions have suggested, but the same issue occurs each time. What is going on???

Answer 1

Michael Birtel wrote:
Here is the log for the last failure. As you see it indicates there is enough room 345g needed, 464G available, but then it fails. I can watch the backup progress, it reaches 345G and then keeps growing till it give out of disk space error. I don't know what "Event store UUIDs don't match for volume: Macintosh HD" implies, maybe this is a clue?
No. It's sort of a warning, indicating that TM isn't sure what's changed on your internal HD since the previous backup, usually as a result of an abnormal shutdown. But since you just erased your TM disk, it's perfectly normal.
Starting standard backup
Backing up to: /Volumes/Time Machine Backups/Backups.backupdb
Ownership is disabled on the backup destination volume. Enabling.
2009-07-08 19:37:53.659 FindSystemFiles[254:713] Querying receipt database for system packages
2009-07-08 19:37:55.582 FindSystemFiles[254:713] Using system path cache.
Event store UUIDs don't match for volume: Macintosh HD
Backup content size: 309.5 GB excluded items size: 22.3 GB for volume Macintosh HD
No pre-backup thinning needed: 345.01 GB requested (including padding), 464.53 GB available
This is a completely normal start to a backup. Just after that last message is when the actual copying begins. Apparently whatever's happening, no messages are being sent to the log, so this may not be an easy one to figure out.
First, let's use Disk Utility to confirm that the disk really is set up properly.
First, select the second line for your internal HD (usually named "Macintosh HD"). Towards the bottom, the Format should be +Mac OS Extended (Journaled),+ although it might be +Mac OS Extended (Case-sensitive, Journaled).+
Next, select the line for your TM partition (indented, with the name). Towards the bottom, the Format must be the same as your internal HD (above). If it isn't, you must erase the partition (not necessarily the whole drive) and reformat it with Disk Utility.
Sometimes when TM formats a drive for you automatically, it sets it to +Mac OS Extended (Case-sensitive, Journaled).+ Do not use this unless your internal HD is also case-sensitive. All drives being backed-up, and your TM volume, should be the same. TM may do backups this way, but you could be in for major problems trying to restore to a mis-matched drive.
Last, select the top line of the TM drive (with the make and size). Towards the bottom, the *Partition Map Scheme* should be GUID (preferred) or +Apple Partition Map+ for an Intel Mac. It must be +Apple Partition Map+ for a PPC Mac.
If any of this is incorrect, that's likely the source of the problem. See item #5 of the Frequently Asked Questions post at the top of this forum for instructions, then try again.
If it's all correct, perhaps there's something else in your logs.
Use the Console app (in your Applications/Utilities folder).
When it starts, click +Show Log List+ in the toolbar, then navigate in the sidebar that opens up to your system.log and select it. Navigate to the +Starting standard backup+ message that you noted above, then see what follows that might indicate some sort of error, failure, termination, exit, etc. (many of the messages there are info for developers, etc.). If in doubt post (a reasonable amount of) the log here.