Re: XFS: SB validate failed

[Stefan Smietanowski <stesmi@stesmi.com>]

Hamid wrote:
> 
>> 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.
>>
> Thanks Stefan, Now it makes real sense.
> 
> I guess I am back to my original question:
> What does 'SB validate failed' indicate and what it really means to my 
> case ?
> 
> fdisk reports the structure of the Jaz disk as:
> 
> $ sudo fdisk -ul jaz7.img
> 
> Disk jaz7.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: jaz7.img1            3072   2091007   2087936   a  SGI xfs
> 9: jaz7.img2               0      3071      3072   0  SGI volhdr
> 11: jaz7.img3               0   2091007   2091008   6  SGI volume
> ----- Bootinfo -----
> Bootfile: /unix
> ----- Directory Entries -----
> 0: sgilabel   sector    3 size     512
> 
> I went ahead and tried to mount Partition 8 from image using the offset 
> and loop options of the mount command:
> 
> $ sudo mount -t xfs -o loop,offset=$((512*3072)) jaz7-partition.img /mnt
> mount: wrong fs type, bad option, bad superblock on /dev/loop1,
>       missing codepage or helper program, or other error
>       In some cases useful info is found in syslog - try
>       dmesg | tail  or so
> 
> And system log says:
> 
> XFS: bad magic number
> XFS: SB validate failed
> 
> So I am guessing I have one of these 3 cases:
> 1- Bad partition table, good file system
> 2- Good partition table, corrupt file system
> 3- Or both gone south!!!
> 
> I checked the man pages of 'vh' on Irix. It seems that the volhdr
> partition is 'usually' 2 megabytes but the disk in question has 3072*512 
> bytes ?
> Can this be a sign of corruption ?
> 
> So where would you start looking at if you wanted to fix this problem ?
> Partition table or the file system ?

Personally I would hexdump the beginning of the disk looking for
the xfs magic of the partition and then try to use that offset
in mount.

One way is : od -t c jaz7.img | grep X | head

Look for X   F   S   B, may be split on two lines for you.

This is what my disk looks like but of course, it's on a DOS
partition:

0077000   X   F   S   B  \0  \0 020  \0  \0  \0  \0  \0  \0  \0   `  \0

Then you have the offset (OCTAL!!) on the left, convert it to decimal,
feed that to mount and see if it mounts. Also check if it's the same
offset as the partition table is telling you or not.

// Stefan