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I have just broke my software RAID 5 Array (build using mdadm) set up by changing one of the HDD partition.

The exact command I used is:

sudo parted -s /dev/sdb mklabel msdos

on one of 4 HDDs in my array.

Is there a way how to fix this HDD and add it back to array without loosing any data?

I'm very new to linux, so now sure how to show you more info about my set up.


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Are you using hardware or software Raid? – Mitch Jun 5 '12 at 11:05
I'm using software raid – Mike Jun 5 '12 at 11:07
up vote 0 down vote accepted

How to add the 4th disk back to the raid? "From Mike's Question in previous comment"

Edit this for your needs:

mdadm --add /dev/md1 /dev/sdf1
mdadm --grow /dev/md1 --raid-devices=4

This then took several hours to reshape the array.

The filesystem the needs to be expanded to fill up the new space.

fsck.ext3 /dev/md1
resize2fs /dev/md1
share|improve this answer
Thanx Subv3rsion that will do it :) – Mike Jun 5 '12 at 12:15
That is how to add a new disk to an array, and expand it to use the additional space, not how to fix @Mike's problem. – psusi Jun 5 '12 at 14:04

You can use a tool named raidextract.

Example usage:

./raidextract --window 1024 --stripe 16 --rotate 6 \
    --start $((0x41C6E79A00)) --length $((4096*1024*64000)) \
    --failed 5 /dev/sd[a-g] | ssh othermachine dd of=RecoveredFilesystem

If you use raidextract to read a filesystem image, you can write the output to a file and run all the standard filesystem tools (tune2fs, e2fsck) on the file. Once you've finished, you can the mount the filesystem with mount -o loop.

For more information, you can read this:

Hope this helps.

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Cheers Subv3rsion, unfortunately I dont have other HDD where can I output 3TB of data to :( I thought that by having Raid-5 one of the HDD is redundant and all data could be easily recovered if one hdd dies. – Mike Jun 5 '12 at 11:38
Well, note that RAID isn't a backup system. – Octávio Filipe Gonçalves Jun 5 '12 at 11:39
One more thing, can you try do a XFS repair? then try to mount it again. – Octávio Filipe Gonçalves Jun 5 '12 at 11:42
ok, I managed to start the raid in degraded state and mount it. Good news is I can access all the data. How to add the 4th disk back to the raid? – Mike Jun 5 '12 at 12:01

If the only thing you did was blow away the partition table with parted, then all you have to do to fix it is to recreate the partition table exactly as it was before. Put parted into sector mode with the unit s command, and you can probably look at the other disks in the array to guess how this one was partitioned.

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