On 2011-11-10 16:11, NeilBrown wrote:
On Thu, 10 Nov 2011 12:50:46 -0400 Chris Purves<chris@xxxxxxxxxxxx> wrote:
On 2011-11-10 12:20, Alexander Kühn wrote:
ddrescue to the rescue!
Get a another new disk, then ddrescue the one with the read error to the new disk.
Assemble the array using the new disk instead of the one with the read error.
You will loose the blocks that can't be read of course.
And in the future do run raid check/scrubbing at regular intervals. ;)
I have tried this already. After cloning the disk with errors, I replaced it with the clone and tried to re-start the array using
mdadm --assemble --force /dev/md1
mdadm assigned the new disk as a spare and said there were only three disks to start the array and so couldn't start it.
After I clone the disk with the error, how precisely should I re-start the array?
This should have worked. So presumably some unstated requirement wasn't met.
Give details. Names of devices, sizes of devices, "mdadm --examine" of
device. Are you using partitions or whole disk ....
The best assemble command would be:
mdadm --assemble /dev/md1 -vv ...list...of.devices..you...want.it.to.include.
NeilBrown
After ddrescue finished, I unplugged the disk with the bad sector (all 4 KB worth), and ran mdadm --assemble --force.
This time the array started up with four disks (three old, one new). I'm not sure why it didn't work the previous time; I must have done something differently.
In any case, it's working now. Thanks to everyone for your assistance. It was a big help knowing that replacing the damaged disk with a clone should work. It saved me a lot of hassle restoring from backup. Now I just need to add a fifth disk and I'll be back to normal.
--
Chris Purves
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