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I'd like to copy data off a disk (EXT2) that's part of a RAID1 mirror (Linux software RAID). When I try to do a manual mount of the disk is complains that it's part of an array. Is there a way to mount the disk in a ro mode without having to create an dummy array?

mount: unknown filesystem type 'linux_raid_member'

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I've move the disk to another machine and issued a mdadm assemble which started a new array which I could mount and recover from. msadm --assemble /dev/md1 /dev/sdx –  Marinus Apr 20 '12 at 20:04

3 Answers 3

up vote 1 down vote accepted

Presuming it is a disk in software RAID, you can start a RAID1 array with just 1 disk, then mount the array.

Any decent hardware RAID controller should also be able to do that.

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It's software RAID on Linux, I already have a RAID array on the host. I need to take care not to mess with the existing array, or update the array so that I can't join the array when I move the disk back. –  Marinus Apr 20 '12 at 11:43

Maybe.

It largely depends on what sort of RAID set it is. Certain versions of Linux MD (software RAID) put the superblock at the end of the RAID device, making it easy for the OS to see the original filesystem and mount it. Others don't. Hardware RAID has similar fun games to play. At least being a RAID1 member it's not (or at least shouldn't be) striped or otherwise mutilated, mangled, or spindled.

Honestly, I'd just make a dummy array (it takes all of about 10 seconds with mdadm) and mount that. You can derp around with mount options and things, but it really isn't worth it.

(Sidenote: "complains that it's part of an array" isn't a good description of the problem; the exact error message would be far more useful)

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I have an array on /dev/md0, do you suggest I do a mdadm --assemble /dev/md1 /dev/sdxx? –  Marinus Apr 20 '12 at 12:29

AFAIK, if the array is stopped you could do that. Is it?

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