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Ext3 partition won't mount

Posted on 2011-02-10
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Hi experts,

I have a server running Ubuntu 10.04 server, which is virtualizing another Ubuntu 10.04 server with qemu / kvm. For some reason somebody yesterday decided to press the power button on the physical server. The virtual server never came back up.

I opened up virt-manager and had a look at my virtual machine. It had just a blinking cursor. I had previously thought maybe it was fsck'ing but it didn't appear to be. I pressed a few buttons on the keyboard, trying to get some input, and all of a sudden it showed a message saying something like "skipping /backup" which is the partition that has all of my files on it. Ubuntu loaded but /dev/sdb was not mounted at /backup. I have not been able to mount it, it gave an error that I can't remember but it may have been about a superblock.

Anyway I'm analysing the partition with testdisk at the moment, but I don't really know what to do from here. Any suggestions? Am I screwed? I have some of the data backed up on an external drive, so that's a bit of a relief. The partition is just a .qcow2 file as well, so maybe there is something I can do from the physical server?

Cheers,
Michael
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Question by:mstrelan
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torimar earned 2000 total points
ID: 34867288
I think you are already going into the right direction: TestDisk is the optimal first step. Try to use it to get the backup superblock locations and then feed this info to fsck:
http://www.cgsecurity.org/wiki/Advanced_Find_ext2_ext3_Backup_SuperBlock

If this won't help, you might also want to try and mount the Qemu image directly in your Ubuntu host system. I never did this myself, and I hope the info given here will suffice:
http://en.wikibooks.org/wiki/QEMU/Images#Mounting_an_image_on_the_host
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by:mstrelan
ID: 34867318
"To search for them, run TestDisk and in the Advanced menu, select the partition and choose Superblock."

No partition available
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by:torimar
ID: 34867373
How did you proceed? Did you boot the VM off a bootable CD?
I recommend Parted Magic for the purpose: www.partedmagic.com

Then follow this guide in order to check whether the partition table may be restored:
http://www.howtoforge.com/data_recovery_with_testdisk
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by:mstrelan
ID: 34867416
The actual data image is on a separate qcow2 image than the operating system, so assumably it is safe to do any fsck / testdisk etc type of stuff without a live disc because the data partition is not mounted.

I have tried to "analyse" in test disk but it did not find any partitions. I am going to try and mount the image directly in the host OS.
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by:mstrelan
ID: 34867547
UPDATE - Good news. On the host OS I was able to mount the disk image and access all my files! Yay!

qemu-nbd -c /dev/nbd0 data.qcow2
partprobe /dev/nbd0
mount /dev/nbd0p1 /mnt/data/
ls -l /mnt/data

Open in new window


Now I just need to know how to get it to mount in the guest OS. I will try the e2fsck with alternate superblock, but I want to take a backup of the disk image first.
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by:torimar
ID: 34867646
That is really good news indeed.

For a backup, I assume it will suffice to copy the qcow2 file to a safe backup location, the continue to work on the original.
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by:torimar
torimar earned 2000 total points
ID: 34867686
If the e2fsck method should not turn out to be viable, you may consider backing up the data files directly from the mounted image, then, inside the VM, format the non-functional disk and "refill" it from the backup - provided that VM has access to the external media used.
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by:mstrelan
ID: 34867727
Thanks torimar, the format / refill method will be my plan b if e2fsck doesn't work. I'm off to buy a bigger hard drive to back up the data. Will be back later to post my results and award points.
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by:mstrelan
ID: 34884741
Ok I wasn't able to fix the disk with testdisk or anything, so the best solution is to mount the image in the host os and scp all the files to a new partition. Thanks torimar for the help
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by:mstrelan
ID: 34884748
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