Insane "backup is too large" message, 4x total space available on drive.

Question

I've read a large number of the "backup is too large" messages in this forum, but none of them seem to explain the message I am getting:
"This backup is too large for the backup volume...requires 2460.3 GB but only 731.5 GB are available."
Under Options, the only disk included in the backup is the internal hard disk (250GB) and the "Total Included" is 161.3 GB as displayed in this screen.
Since I can backup my "entire" disk 4 times in the space remaining, this doesn't make any sense.
Suggestions of blowing away and starting over would just be completely counterproductive to the idea of having a backup system and I really need to fix this issue and not lose the archived history which I reference (regularly).
The time machine backup is stored on a Mirrored 2x1TB system, so only 270GB is currently being taken up by backups.
Thanks in advance for any thoughts,
Barney

Answer 1

All of the stuff I've read seems to indicate that Time Machine should be able to sort this issue out normally.
Yes, but you should see the long "preparing" and "deep traversal" only for a good reason -- if there's no crash, the incremental backups should be pretty quick.
In this case there was a crash, which likely is in the vicinity of when the last backup succeeded, so I do confirm this as the likely cause.
I'm wondering if one of those crashes managed to corrupt the File System Event Store. That might explain what's going on, as TM estimates how much space it's going to need from there.
I run drive repair fairly regularly and have just before and just after this crash...its amazing how often permissions get scrambled even when there are no crashes or strange events...but that's another topic.
The other thing that repeated crashes might do is, corrupt your disk(s). I'd recommend a +Repair Disk+ on your TM volume and a +Verify Disk+ on your internal HD. If the internal needs repair, you'll have to boot from your Leopard disc and use it's copy of Disk Utility.
I've never had anything other than Permissions issues with the internal drive. I've had external drive failures, but recently replaced all of my old drives (hence the raid sets) so this should not be a major issue in the future.
Let me ask this: you say it crashes a lot, but are these OS crashes or programs that get into tight loops that can't be force-quit, so you do a force power-off?
A lot is probably an extreme statement, but I'm contrasting it to how stable Mac traditionally is (I develop in all three of the major universes). I have to reboot a few times a day due to instability, but sudden stop/force shutdown is more like once every couple of weeks on average.
Also, rarely is it my programming that directly contributes to the crash or force quite situation. Its normally strictly an OS crash [grey quit unexpectedly box] or other software hang [can't force quite or kill]. I just attribute this to the heavy load that the computer is constantly under and the influx of relatively unstable development tools (XCode alone crashes a few times a day in the middle of work, and its a pretty stable piece of software).
I do hate to say it, but if you can't reduce the frequent crashes, you may want to use a different backup app, such as CarbonCopyCloner (which I use in addition to TM), SuperDuper!, or the like. Their incremental backups run much longer than a "normal" TM incremental backup, as they don't use the internal log, but also won't get confused by a corrupt FSEventStore.
The Time Machine has really been a dream come true for development. I use source control and offline storage and full backups in addition to TM, but TM brings with it an incredible ease of browsing and analying file history and progression. I could see it being better, but I've found few things as easy to use and readily accessible as TM.
I'll run the tests from your previous posts since that has the added benefit of not losing the backup data. If its possible to just reset the system when something freaks out then I'm okay with that. I'd just hate to constantly reset all the history with it as well.
Thanks again for all of the feedback and I'll report back soon on success or failure.
Barney