TM is very slow even for tiny backups

Question

Hi,
I've been using Time Machine for quite some time now, a year or more. It was fine at first, no problems doing the initial backup and everything works fine.
But over time it seems to have become slower and slower. Now even when the amount of data to back up is very small (a few megabytes), the whole process takes 25 minutes or more. When the backup is larger (100mb or more), the backup often takes longer than an hour. Time Machine spends more time backing up than it does waiting in between backups.
I see nothing in the Console logs that indicates a problem. Here's what a typical small backup looks like:
14/03/09 7:47:27 AM /System/Library/CoreServices/backupd[1216] Starting standard backup
14/03/09 7:47:36 AM /System/Library/CoreServices/backupd[1216] Backing up to: /Volumes/Time Machine Backups/Backups.backupdb
14/03/09 7:49:47 AM /System/Library/CoreServices/backupd[1216] No pre-backup thinning needed: 222.2 MB requested (including padding), 71.15 GB available
14/03/09 7:59:00 AM /System/Library/CoreServices/backupd[1216] Copied 140670 files (12.4 MB) from volume alex.
14/03/09 7:59:06 AM /System/Library/CoreServices/backupd[1216] Copied 140680 files (12.5 MB) from volume Macintosh HD.
14/03/09 8:00:23 AM /System/Library/CoreServices/backupd[1216] No pre-backup thinning needed: 237.2 MB requested (including padding), 71.14 GB available
14/03/09 8:06:21 AM /System/Library/CoreServices/backupd[1216] Copied 110501 files (13.9 MB) from volume alex.
14/03/09 8:06:32 AM /System/Library/CoreServices/backupd[1216] Copied 110609 files (14.0 MB) from volume Macintosh HD.
14/03/09 8:12:46 AM /System/Library/CoreServices/backupd[1216] Starting post-backup thinning
14/03/09 8:13:03 AM /System/Library/CoreServices/backupd[1216] Deleted backup /Volumes/Time Machine Backups/Backups.backupdb/TellyMac/2009-03-13-072250: 71.14 GB now available
14/03/09 8:13:03 AM /System/Library/CoreServices/backupd[1216] Post-back up thinning complete: 1 expired backups removed
14/03/09 8:13:03 AM /System/Library/CoreServices/backupd[1216] Backup completed successfully.
As you can see, well over 20 minutes from start to finish. The whole time it's happening, backupd thrashes the disk and uses 20-50% CPU, so it's not fun.
Surely this is not normal? I never measured it before, but I'm certain it was many times faster before.

Answer 1

awhs wrote:
The pre-backup and copying time is now very short, less than a minute.
Ah, that's more like it.
Post-backup thinning takes almost all of the 10 minutes. Removing the IMAP folder reduced the size of the TM data by around 10gb. So the issue here seems to be the number of files. I suspect there is something else in my old backups (which go back around 12 months) that has a large number of small files, just like the IMAP folder, and that is contributing to the 10 minute post-backup time.
Not exactly. Post-backup thinning is just TM deleting "expired" backups -- hourlies over 24 hours, dailies over a month. Once it's down to deleting only a few at a time, it should be much faster. What may be happening is, the old backups still contain thousands of the "multi-links" from the IMAP files. Once they get weeded out, each one will be deleted much faster.
A couple of things to try:
Download the TimeTracker app, from www.charlessoft.com.
It shows most of the files saved by TM for each backup (excluding some hidden/system files, etc.). This will tell you what, specifically, is being backed-up now.
Do a +Repair DIsk+ (not Permissions) on your TM drive via Disk Utility (in your Applications/Utilities folder).
Then watch both the number of backups deleted and how long it takes to delete them.