Has anyone here who's running Mountain Lion (10.8.2 in this case) experienced any issues with EFI partition information on external disks?

When I scan the top level drive for my external hard drive (that I use for my bootable backup) I get the following error message:



This can't be repaired. The underlying individual volumes check out fine.

A search on the Apple support site shows quite a few people reporting the same issue which appears to be peculiar to ML.
Anyone on here encountered it?
The drive was originally formatted under Snow Leopard and was fine there. I'm somewhat reticent to reformat the drive under ML as the Apple discussions appear to suggest that doesn't fix the problem anyway.

ARE you having problems booting this volume?

If not...

(I don't have ML)...

can you confirm the edition of DU in SL is different (earlier) to that in ML?

If so I'd be inclined to assume there's a bug in the ML edition of Disk Utility.

HTH.

Ian.

When you get those sorts of errors the only thing that you can do is reformat it. Do a clone of the drive and then reformat and reinstall your data.

I'm somewhat reluctant to reformat the drive for what appears to be an issue with Disk Utility rather than the drive itself.

The drive mounts fine on the desktop and the 'Verify Disk' checks on the individual volumes come back fine. I haven't tried booting off it recently as it's the drive I use for an off-site backup.

As I said in the OP, a search on the Apple Support discussion boards brings up similar or identical problems from a number of different users. Disks checked in Snow Leopard or Lion show no errors, it's only the version of DU in mountain lion that shows a problem.
I've raised a support ticket with Apple (seeing as I only got ML at the end of last month) so it's still in the 90 day support period.

I can appreciate not wanting to reformat, but if it is a problem with disk utility the only way of replacing is to reinstall the OS. Have you tried any other drive utility? Like Drive Genius or Tech Tool Pro? They can also find problems, but might also be unable to fix them. It sounds more like a problem with the file allocation table, or its equivalent. The files could be fine but the records of where they are might be corrupted. If there is a problem with the disk reformatting will mark those sectors as bad so stopping you saving data there. I think that I had a similar problem with a drive some years ago. Formatting did not fix it and so the drive was replaced.

If it is for an offsite back up then what if there are problems with the back ups. You will simply have been wasting time backing up. If you have a support ticket with Apple then they are the experts.

Amnesia10 wrote:

"The files could be fine but the records of where they are might be corrupted. If there is a problem with the disk reformatting will mark those sectors as bad so stopping you saving data there..."

That is NOT correct. Disk Utility cannot identify and "spare" (mark as bad and render unavailable) bad blocks/sectors.

Drive Genius however can.

To date it seems you've neither checked bootability nor established whether DU in ML is a later version than the SL edition

I'd not do anything at all until you've checked both of the above points. If it transpires the drive is not bootable then consider checking with Drive Genius.

Aside:
(a) If there is a bug in ML's version of DU then reinstalling will (obviously) not resolve your particular issue.

davrosG5 wrote "The drive mounts fine on the desktop and the 'Verify Disk' checks on the individual volumes come back fine."
(b) As disk VERIFICATION does not indicate a problem on this volume...
(c) What caused you to run REPAIR? (or have I misunderstood your posts?)

Prior to performing a clone I run Disk Utility over the source and destination disks before hand to check for issues as there is little point in backing up to or from a duff disk.
This was the first time I've done a clone backup since installing ML so it's the first time I've used DU in ML.

Under SL if you clicked on the disk (rather than the individual volumes) and clicked Verify Disk it would scan each of the volumes present on the disk in sequence so that's what I did when I ran my scan in ML. However, the behaviour in ML is different. Instead of scanning each volume on the disk in turn it produced the partition map scan I posted the screenshot of in my OP. When the verify failed I naturally clicked on repair to see if it would fix the issue (which also failed). That suggests to me that the version of DU in ML is indeed different from that in Snow Leopard.

Having previously seen odd erroneous issues with DU on previous machines I thought it would be a good idea to do a quick internet search for the error message and there were rather a few discussions on the apple support site and other mac forums about the issue which suggests to me that it might not be a genuine error but rather a bug in the ML version of DU.

I'll +1 Drive Genius in this instance. Grab a copy of that and run a repair using that.

Also try Disc Warrior. Both these apps have got me out of scrapes in the past. These should be your first port of call. Also buy a disk for Time Machine duties if you have not done so already. Do that now.

davrosG5,

FYI, Disk Utility in Snow Leopard is...

Version 11.5.2

I've just checked.

My SL version of Disk Utility was 11.5.2. The ML version is 13 so it is definitely a new version.

I have an internal drive for TM backups. The affected disk is external so I can take it off-site.
I've got old versions of both Drive Genius and DiskWarrior. Haven't quite got round to getting them up to date. Looks like it might be an idea.

Spoke to Apple support. Aside from their catastrophically broken hold music system I was reasonably impressed.

They were flumoxed by the problem so it's being escalated to a software engineer to investigate.
I'm pleasantly surprised their first response wasn't to just tell me to reformat the drive. So, the saga unfolds.