MyBook failing with Time Machine, how to diagnose?

[neilw]

I have a couple of WD MyBook Home Edition drives that use for Time Machine backup with my 21.5" iMac (I alternate the drives every couple of weeks, and keep one off-site). I've been experiencing intermittent problems with both, but the one I'm using now is really misbehaving badly. The drive is connected via FW400, though I've experienced similar behavior via USB, and the drives also did this to some extent with my old iMac G5.

Basically, Time Machine backups will fail before getting very far, though Time Machine doesn't provide any significant feedback as to what happened. At this moment I have about 450 MB to back up. TM will typically get to the point where it copies the first little bit, then hangs: e.g., it stops at "2.2 MB of 456 MB". After a while, it bails out, cleans up, and schedules the next backup.

I cannot figure out any pattern to this. I did originally succeed at getting the initial backup (about 200 GB) to work, and then the backups worked fine for a while. In the past, when the drives have acted up like this, I've been able to get them to start working again, sometimes, by just unplugging the drive (including power) for a while. Right now, though, it's being quite stubborn.

How can I diagnose what's going on? Is it the drive itself, or the enclosure that's misbehaving? If the latter, I can just get a new enclosure and transfer the drive. But I need to understand what's going on first.

Any insight would be appreciated.

 

[neilw]

Here's the log from my most recent backup attempt:

Starting standard backup
Backing up to: /Volumes/xxxxxxx/Backups.backupdb
Node requires deep traversal:/Users/xxx/Pictures/old iPhoto Library reason:must scan subdirs|missed reservation|
No pre-backup thinning needed: 1.08 GB requested (including padding), 290.23 GB available
Copied 531 files (2.0 MB) from volume Macintosh HD.
No pre-backup thinning needed: 578.0 MB requested (including padding), 290.23 GB available
Copied 283 files (517 KB) from volume Macintosh HD.
Starting post-backup thinning
No post-back up thinning needed: no expired backups exist
Backup completed successfully.

It's actually saying it completed successfully, despite the fact that it only copied 2.5 MB out of "a lot more". Is this working or not? If I run TM over and over, it keeps saying it needs to do a total of 462.8 MB, but the progress bar never gets past a couple of MB. Doesn't sound like it's working to me, even though it reports success each time....