Recover mdadm raid1 data after recreate new array over old

Murz · 12-11-2011, 01:46 PM

I had the raid1 (mirror) mdadm working array /dev/md1 with one failed disk, so /dev/sda5 is active and /dev/sdb5 is missing (partition is deleted), and I try to mark second drive as failed.
But I do the mistake: create new array over old data instead of run:

Code:

# mdadm --stop /dev/md1
# mdadm --create /dev/md1 /dev/sda5 ...
instead of
# mdadm --assemble /dev/md1
or 
# mdadm --run /dev/md1

So, this create command overwrite the superblock and other info about old md1 array.
How can I recover data from old md1 array now?

smallpond · 12-13-2011, 10:12 AM

Quote:

Originally Posted by Murz

I had the raid1 (mirror) mdadm working array /dev/md1 with one failed disk, so /dev/sda5 is active and /dev/sdb5 is missing (partition is deleted), and I try to mark second drive as failed.
But I do the mistake: create new array over old data instead of run:

Code:

# mdadm --stop /dev/md1
# mdadm --create /dev/md1 /dev/sda5 ...
instead of
# mdadm --assemble /dev/md1
or 
# mdadm --run /dev/md1

So, this create command overwrite the superblock and other info about old md1 array.
How can I recover data from old md1 array now?

This post:
http://kevin.deldycke.com/2007/03/ho...d-superblocks/

claims that if you recreate your original RAID correctly, that the content will not be destroyed.
Before doing anything it would be a good idea to make a binary copy of the whole partitions and only work on the copies. Something like:

Code:

dd if=/dev/sda5 of=/dev/sdz1 bs=1m

Murz · 12-15-2011, 05:04 AM

Quote:

Originally Posted by smallpond

This post:
http://kevin.deldycke.com/2007/03/ho...d-superblocks/

claims that if you recreate your original RAID correctly, that the content will not be destroyed.

Thanks, I recreate my raid, but after that it don't want to mount correctly. But I run fsck /dev/md1, it found and recover many errors, but after that I correctly mount it and see my files.
I found info that mdadm metadata version 0.90 save superblock at end of drive, but 1.2 version - at first of drive, so after I create over old mdadm 0.90 mdraid new 1.2 mdraid, it rewrite the start of ext3 filesystem. But fsck found copies and recover it.