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How to rescue a partially damaged hard disk
The HD of my work computer was broken. It failed to read some
sectors, while working ok otherwise. The following text shows, how I
recovered the filesystem. A couple of years
later Florian Hackenberger
pointed out, that
My completely manual method
I got myself a second computer with a big empty harddisk and a running linux. I installed the broken HD on the secondary IDE channel. My plan was to get a raw image of the main partition, mount it again with linux's loop option and copy the data onto a new HD.
The broken HD is /dev/hdc . Partition 1 is the / file system. Partition 2 was my swap device. I read in blocks of 1024 bytes.
[root@base /tmp]# dd if=/dev/hdc1 of=1 bs=1024 dd: /dev/hdc1: Input/output error 7332+0 records in 7332+0 records out
The first part of the disc was read. Obviously the
7333th sector of the HD is damaged. I tried a
[root@base /tmp]# dd if=/dev/hdc1 of=2 bs=1024 skip=7333 dd: /dev/hdc1: Input/output error 385907+0 records in 385907+0 records out
We encountered another broken sector. We just skip it. Be carefull about the new skip value. You have to sum up all previous skip values: 7333 + 385908 = 393241 !
[root@base /tmp]# dd if=/dev/hdc1 of=3 bs=1024 skip=393241 1219527+0 records in 1219527+0 records out
Now we finally managed to read up to the end of the HD. Now we have three pieces each with a hole of 1KB. Now we make ourself 1K of plain data.
[root@base /tmp]# dd if=/dev/zero of=z bs=1024 count=1 1+0 records in 1+0 records out
Now we copy the files together and we have a nearly perfect image of our broken HD.
[root@base /tmp]# cat 1 z 2 z 3 > hd
We should now run fsck on the image, because there will be at least 2 errors resulting from those two 1K holes, which we filled with 0 values.
[root@base /tmp]# fsck.ext2 -a hd hd contains a file system with errors, check forced. .... with some repair msgs from fsck
We now can mount this HD image to /mnt/old.
[root@base /tmp]# mkdir /mnt/old [root@base /tmp]# mount hd /mnt/old -o loop
Our new HD is mounted on /mnt/new. We have already partitioned it with
[root@base /tmp]# (cd /mnt/old; tar c *)|(cd /mnt/new; tar xv)
One small problem is left. The new HD is not able to boot by now. We make a boot disk from the kernel image.
[root@base /tmp]# cat /mnt/new/vmlinuz > /dev/fd0
Now we have to set the root device the boot disk should boot from. In
my case this is
[root@base /tmp]# rdev /dev/fd0 /dev/hda1
Congratulations. We are finished. We have to install the new HD back
into our computer and boot once from the boot disk. Then I execute a
Now we just have to clean up our files in the
A tool which automates the dump of the broken disk
is ddrescue. It
will intelligently skip over broken areas on the disk and can attempt
to read a sector multiple times to increase the chance of getting
Restoring the partition table
If your partition table was destroyed, chances are good that you may be able to create a new table from information inside your partitions. I can recommend the program testdisk.
Restoring a filesystem
Collin Park describes his attempt to make a corrupted FAT filesystem readable again.
Monitor your harddrive
The smartmontools have a daemon which monitors your hard drive via the S.M.A.R.T interface, which should be present on all modern drives. In case of failure it can perform various actions, like sending email, shutting down the system etc. so the drive won't be damaged any further.
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