Mac HFS+ - what cause volume to become unmountable?

[Allasso]

Hello,

I have an external HDD formatted for Mac (HFS+). It has become corrupted and is unmountable. Running some software recovery tools seems to indicate that most of the files are pretty much intact, and may be recoverable, but it would seem to me that there is a problem causing it to not be able to mount, and I am interested in what causes this, if only for educational purposes. For example, is there data in the volume header that was corrupted that makes the data partition unmountable, or is this a problem with the partition itself? It would seem to me that if I can get the partition to mount, I would have a lot better chance at recovering files intact, with proper file names, and even if they are fragmented.

I am more interested in finding out the theory and structure behind what makes these things tick, and possibly implementing a low level solution, than just running recovery tools on it, that so far will give me disoriented files without original filenames, and will not recover fragmented files. As I eluded, I am as much or more interested in the educational benefit, as I am actually fixing the drive.

Many thanks,

Allasso

[labtech]

Did you or anybody else using the drive notice any uncommon signs, that could be perceived as problematic? For example: drive/data access slowing down, system freezing, any strange sounds coming out of the drive, etc.

Was the drive removed or ejected from the system without dismounting it first?

[Allasso]

Did you or anybody else using the drive notice any uncommon signs, that could be perceived as problematic? For example: drive/data access slowing down, system freezing, any strange sounds coming out of the drive, etc.

No. The only "warning" was basically when the failure was occurring: the drive would not mount using firewire, but mounted using USB (once). At that time, the files could be seen in the finder, but could not be copied (gave some kind of error message, don't recall what). After that one time of mounting, it never mounted again, though (fortunately) it shows up in Disk Utilities*/dev/, but only when connected to USB. There is no sign of it when trying to connect via firewire.

Was the drive removed or ejected from the system without dismounting it first?

undoubtedly that has happened at times in the past, but the owner doesn't recall that happening immediately before the failure.

Last edited by Allasso on June 12th, 2012, 10:02, edited 1 time in total.

[Allasso]

I thought I would post the output from mmls:

Code:

mmls /dev/disk3
MAC Partition Map
Offset Sector: 0
Units are in 512-byte sectors

     Slot    Start        End          Length       Description
00:  -----   0000000000   0000000000   0000000001   Unallocated
01:  00      0000000001   0000000063   0000000063   Apple_partition_map
02:  Meta    0000000001   0000000004   0000000004   Table
03:  01      0000000064   0000262207   0000262144   Apple_Free
04:  02      0000262208   0976773151   0976510944   Apple_HFS
05:  03      0976773152   0976773167   0000000016   Apple_Free

[harddrivespecialist]

Drive might have one of several problems such as; bad sectors, scratches or partition corruption...

[labtech]

Can run MHDD to rule out few things. Then if all good with the drive's hardware, check out something like DiskWarrior.

[Allasso]

Can run MHDD to rule out few things. Then if all good with the drive's hardware, check out something like DiskWarrior.

It doesn't appear that MHDD will work on Mac :-/ (without emulation)