I've made a mess of my raid setup and am desperately trying to save it. The setup is RAID-5 on 3 SATA disks. Problems started with one of the disks getting unrecoverable read errors. Unfortunately I was away on a trip and the machine was used by my family while this was going on :( Array consists of three devices: /dev/sda2, /dev/sdc2, and /dev/sdd2. When I got back from the trip I found the following: 1. Two disks were removed from the array, leaving only /dev/sda2; 2. When either of the two was added, the array would start; 3. One combination of two disks (/dev/sda2 + /dev/sdd2) aproduced a running /dev/md0 with a proper ext3 filesystem seen on the drive (even passing fsck); At this point I added /dev/sdc2 and the reconstruction started. However did not complete, since /dev/sdd2 has unrecoverable errors. Reading the list archives I figured I need another drive to ddrescue /dev/sdd2, then perform the reconstruction. However at some point during/after the reconstruction the situation has changed. Now both /dev/sdc2 and /dev/sdd2 are marked as spare drives (see mdadm -E output below) and I cannot start the array. I think /dev/sdd2 should be in sync with /dev/sda2, but how can I bring it back (it used to be device 2)
I recently had similar problem with a 6 disk array, when one died and another gave read errors during reconstruction, this is my experience:
I was able to recover most data reassembling the array and copying data from it to another storage; I used a command like:
mdadm --create /dev/md3 --assume-clean --level=5 --raid-devices=6 --spare-devices=0 /dev/sda4 /dev/sdb4 /dev/sdc4 /dev/sdd4 /dev/sde4 missing
where /dev/sdf4 was the dead disk, which i left out as missing, and /dev/sdb4 was the one which gave read errors; missing a disk avoids starting the reconstruction. It's important to set the md device in read-only mode (if supported by mdadm version can use the --readonly option directly with the --create command, see man mdadm), and to mount the device readonly.
This mostly worked for me (lost 100Gb over 2.5Tb) I hope you can recover your data. Regards -- Cordiali saluti. Yours faithfully. Giovanni Tessore -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
