Re: XFS: SB validate failed

[Stefan Smietanowski <stesmi@stesmi.com>]

Stefan Smietanowski wrote:
> Hamid wrote:
>> Stefan Smietanowski wrote:
>>>
>>> Are you dd'ing the whole disk or just the partition(s) you want ? I
>>> recommend just doing the partition(s) into seperate files. I'm uncertain
>>> if loopback nowadays handles partitions or not. I know it didn't before
>>> but there were patches back then.
>>>
>>> // Stefan
>>>
>> I did the whole disk under Linux:
>>
>> $ dd if=/dev/sdb of=disk.img conv=noerror,sync
>>
>> This is how fdisk sees my image:
>>
>> $ sudo fdisk -ul disk.img
>> Disk disk.img (SGI disk label): 255 heads, 63 sectors, 0 cylinders
>> Units = sectors of 1 * 512 bytes
>>
>> ----- partitions -----
>> Pt#    Device  Info     Start       End   Sectors  Id  System
>> 8: disk.img1            4096   3915599   3911504   a  SGI xfs
>> 9: disk.img2               0      4095      4096   0  SGI volhdr
>> 11: disk.img3               0   3915599   3915600   6  SGI volume
>> ----- Bootinfo -----
>> Bootfile: /unix
>> ----- Directory Entries -----
>> 0: sgilabel   sector    2 size     512
>>
>> I could mount the image of the healthy disk using:
>>
>> $ sudo mount -t xfs -o loop,offset=$((512*4096)) disk.img /mnt
>>
>> and I was able to browse the content of /mnt :)
> 
> Excellent, that's one step on the way.
> 
>> Trying to mount the whole image didn't work. I was hoping I could do 
> 
> Well of course, since "mounting" implies a filesystem and how is
> the mount command to know which partition you want to mount and
> what filesystem it is to mount? For all it knows you can have 4
> partitions with 4 different filesystems on it and how is it to
> choose the correct one?
> 
> Remember mounting = enabling a filesystem (in a device or file or...)
> to be used via a filesystem driver and exported to a mountpoint (/mnt
> for example).
> 
> In order to do what you're really after you either use your offset
> trickery OR use a kernel that can mount partitioned loopback OR write
> the image to another disk.
> 
>> that so it gives me the possibility of modifying the partition table 
>> of the bad disks that refuse to mount under either OS.
> 
> If you want to play with the whole device (ie not files) then you can
> just run your favorite partition program on your image file or your
> favorite binary patching program on the image file.
> 
>> Basically I want to play with bad disks' images to see if I can 
>> recover any data without actually modifying the disks.
>> Is there any work around for this ?
>> Should I create a device (rather than a loop) for the whole image ?
> 
> I think you have the terminology a little mixed up.
> 
> If you mount a something without supplying -o loop "mount" will assume
> the filesystem resides in a DEVICE.
> 
> If you mount a something WHILE supplying -o loop you tell "mount" that
> it should mount it using a loop device. Note device here, it's trickery
> really as what it does is that "mount" will FIRST create a new device
> node "/dev/loop0" for example and then it will mount from that device
> node.
> 
> So "should I create a device .." is a little mixed up as that's what
> mount is doing deep inside.
> 
>> I should mention that creating the whole disk image by using dd under 
>> Irix6.5 and using the same mount command as above in Linux didn't 
>> work! Something might have gone wrong during the file transfer from 
>> Irix to Linux. If I get a chance I'll try it again.
> 
> If you do, then create a checksum (sha1sum och md5sum or something) and

And here's me replying to myself...

The command that's really use deep down inside is losetup, have a look
at the manpage.

// Stefan