Corrupt qcow2 image, recovery?

Corrupt qcow2 image, recovery?

[Christian Nilsson]

Hi!

I'm running kvm / qemu-kvm on a couple of production servers everything (or at least most things) works as it should.
However today someone thought it was a "good" idea to restart one of the servers and after that the windows 2k3 guest on that server don't boot anymore.

kvm on this server is a bit "outdated": "QEMU PC emulator version 0.9.1 (kvm-83)"
(I guess this is one of the qcow2 corruption bugs, and i can only blame myself for not upgrading kvm sooner.)
The guest.qcow2 is a 21GiB file for a 60GiB disk

i have tried a couple of things kvm-img convert -f qcow2 -O raw guest.qcow2 guest.raw
this stops and does nothing after creating a guest.raw that is 60GiB but only using 60MiB

so mounted the fs from another server running: "QEMU PC emulator version 0.12.1 (qemu-kvm-0.12.1.2)"

and run qemu-img with the same options as above and after a few secs got "qemu-img: error while reading"
and the same 60MiB used by guest.raw

i also tried booting qemu-kvm with a linux guest and this qcow2 image but only get I/O Errors (and no partitions found)

# qemu-img check guest.qcow2
ERROR: invalid cluster offset=0x100000a000          
ERROR OFLAG_COPIED: l2_offset=ee73 refcount=1       
ERROR l2_offset=ee73: Table is not cluster aligned; L1 entry corrupted
ERROR: invalid cluster offset=0x11d441000800000                       
ERROR: invalid cluster offset=0x11d616000800000                       
ERROR: invalid cluster offset=0x11d686000800000                       
ERROR: invalid cluster offset=0x11d953000800000
................(and a loot more in this style, full log can be provided if it would be of help to anybody)



is there any possibility to repair this file, or convert it to a RAW file (even with parts padded that are not "safe" from the qcow2 image), or as a last resort, are there any debug tools for qcow2 images that might be of use?

I have read up on the qcow fileformat but right now i'm a bit short of time, i need the data in this guests disk image, or at least the MS SQL datafiles that are on this disk) i have also checked the qcow2 file and it do contain a NTLDR string and a loot of other NTFS recognized strings so i know that all data is not gone. the question is how can i access it as a Filesystem again?


Any help would be appreciated!

Regards
Christian Nilsson

Re: Corrupt qcow2 image, recovery?

[RW]

Liang Guo gave me this advice some weeks ago:

> you may use kvm-nbd or qemu-nbd to present kvm image
> as a NBD device, so
> that you can use nbd-client to access them. eg:
>
> kvm-nbd /vm/sid1.img
> modprobe nbd
> nbd-client localhost 1024 /dev/nbd0
> fdisk -l /dev/nbd0

Didn't work for me because I always got a segfault
but maybe it work's for you.

- Robert




On 03/16/10 19:21, Christian Nilsson wrote:
> Hi!
> 
> I'm running kvm / qemu-kvm on a couple of production servers everything (or at least most things) works as it should.
> However today someone thought it was a "good" idea to restart one of the servers and after that the windows 2k3 guest on that server don't boot anymore.
> 
> kvm on this server is a bit "outdated": "QEMU PC emulator version 0.9.1 (kvm-83)"
> (I guess this is one of the qcow2 corruption bugs, and i can only blame myself for not upgrading kvm sooner.)
> The guest.qcow2 is a 21GiB file for a 60GiB disk
> 
> i have tried a couple of things kvm-img convert -f qcow2 -O raw guest.qcow2 guest.raw
> this stops and does nothing after creating a guest.raw that is 60GiB but only using 60MiB
> 
> so mounted the fs from another server running: "QEMU PC emulator version 0.12.1 (qemu-kvm-0.12.1.2)"
> 
> and run qemu-img with the same options as above and after a few secs got "qemu-img: error while reading"
> and the same 60MiB used by guest.raw
> 
> i also tried booting qemu-kvm with a linux guest and this qcow2 image but only get I/O Errors (and no partitions found)
> 
> # qemu-img check guest.qcow2
> ERROR: invalid cluster offset=0x100000a000          
> ERROR OFLAG_COPIED: l2_offset=ee73 refcount=1       
> ERROR l2_offset=ee73: Table is not cluster aligned; L1 entry corrupted
> ERROR: invalid cluster offset=0x11d441000800000                       
> ERROR: invalid cluster offset=0x11d616000800000                       
> ERROR: invalid cluster offset=0x11d686000800000                       
> ERROR: invalid cluster offset=0x11d953000800000
> ................(and a loot more in this style, full log can be provided if it would be of help to anybody)
> 
> 
> 
> is there any possibility to repair this file, or convert it to a RAW file (even with parts padded that are not "safe" from the qcow2 image), or as a last resort, are there any debug tools for qcow2 images that might be of use?
> 
> I have read up on the qcow fileformat but right now i'm a bit short of time, i need the data in this guests disk image, or at least the MS SQL datafiles that are on this disk) i have also checked the qcow2 file and it do contain a NTLDR string and a loot of other NTFS recognized strings so i know that all data is not gone. the question is how can i access it as a Filesystem again?
> 
> 
> Any help would be appreciated!
> 
> Regards
> Christian Nilsson
> --
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