G'day MTAU.

I'm having some really strange issue with Time Machine which started about 2 weeks ago - I didn't act much on it in the hope it'd work itself out, but that isn't the case. Every time I go to backup, it begins preparing itself, Spotlight begins indexing something, TM starts backing up (last attempt it got about 26megs into 2.5gigs) but then randomly stops with this error message...


The Time Machine menu also displays "Lastst Backup: Failed..."

Console log as follows...

(In this console log I have used the 'Find and Replace' on my name with Jazzdogg, don't exactly want to put my full name out on the forum )

The error it has with indexing a file seems to be different every time... the /DOS/Rebel/ folder it keeps pointing to didn't exist 3 days ago so I know that isn't the source of the issue.

I run my Time Machine backups via my Airport Extreme (802.11n Fast Ethernet revision) to a 320gig USB caddie. My brother also backs up off the same device and is reporting the same issues are happening to him when he pops by and backs up his machine.

I can browse the USB disk via Airdisk in Finder just fine, even other hard drives.... just can't back up, and it has worked before.

Does anyone have any suggestions after seeing the logs? I'd rather not wipe the HD and start again (as my brother also shares my TM HD too) if it's possible to fix it.

Many thanks in advance

All I can think of is that Spotlight is trying to index the drive, which at the same time is trying to be used by Time Machine.

Try dragging your drive to the privacy folder within the Spotlight preferences and see if that resolves your issues.

This is just a hunch, I also don't know what console logs mean.

Your Time Machine backup sparseimages are corrupt. You will need to re-create the archives from scratch.

Time Machine support by the AEBS is an officially un-supported feature, and the reason why it is unsupported is that some USB bridge-chips used in external enclosures do not work as expected with Apple hardware. Time Machine requires a 100% stable connection; if the connection disappears even momentarily during the course of a backup write, and the Time Machine host does not receive the proprietry error-check-fail response (which is only present in Time Capsule and Mac OS X Server 10.5.2) then the archive becomes corrupt.

Sorry muchacho. Time to start again. Invest in a Time Capsule if you want remote-shared backups to be reliable.

See more info in this TidBits article.

Interesting. Thanks Brains, that clears things up a fair bit. It's strange the Airport wouldn't report a error-check-fail response in the way a server would. Are you also suggesting that a better quality external hard disk may operate more reliable than a cheaper caddie? I'm using an Xcraft caddie I purchased from my fav online computer shop and used one of my older 320g HDDs - I thought it would be a great way to reuse older equipment that isn't exactly obsolete. Would a... say Western Digital MyBook Studio Edition work more reliable than my Xcraft for TM via Airdisk purposes, or is using Airdisk for such a function isn't great?

Would WiFi have any play in reliability (except for the first backup, of course) over ethernet for TM usage, or is it the Airport to HDD link? I also use a D-Link USB hub (unpowered, but seemingly fine - shows green lights to indicate it isn't underpowered) sharing to two Xcraft caddies and a USB printer - would that have any effect on reliability, too?

It isn't as convenient but should I consider connecting the disk directly via USB for any of my backups instead of Airdisk? (even though doing so would mean I'd do less backups, it'd mean much higher reliability, correct?)

I find it interesting that not only my Sparse Image but my brothers has become corrupted, even though we don't access the TM at the same time...

Yes, you should stick to using a directly-connected drive to make use of Time Machine, unless you want to add a TimeCapsule to the armada and keep it solely for your backups of the house's Macs. Keep the AEBS and any drive you hang off it as network storage only.

Interestingly, I plugged the USB caddie directly into my MBP and repaired the disk though Disk Utility and plugged the caddie back into the Airport and it's happily running again so far... backing up a lot of a data and seems to be working fine again. If it is successful would you still recommend I format the the drive and do physically connected USB backups?

Edit: Wow it was doing so well... a few hundred megs into the update it kicked it. USB seems to be the way, then Thanks to Brains and leon for their input!