[CentOS] Reassemble software RAID
maillists at conactive.com
Tue Dec 2 18:31:19 UTC 2008
Scott Silva wrote on Sat, 29 Nov 2008 14:52:18 -0800:
> Before you do anything, can you access the LVM's on /dev/sdb2?
> If so, make sure you back everything up as you will probably need to start
> over on the raid arrays. Worse case you will need a third drive for temporary
> storage. Best case, you can create new arrays on /dev/sda with only one
> member, migrate the data from sdb to sda, and then add sdb to the arrays.
Thanks, I overlooked this message some days ago. I didn't need to back anything
up. I created the new RAID structure on disk 1 with missing mirrors and kept
the old structure on disk 2 that was now merely acting like normal
partitions/LVM. The hard part then was getting it to boot from the RAID. I
didn't know that the root device path is hardcoded in initrd and an error
message of "cannot switch to root" is not very helpful (now, a helpful error
message would have been just slightly different: "cannot switch to root path
/dev/md1"). I found that out when I finally unpacked the initrd. Once I knew
that getting it to boot was easy.
Then I moved all data to the new LVM/RAID partition on disk 1 and finally
copied the partition table to disk 2 and added the missing mirrors to the md
devices. It took actually a bit more copying to and fro as I experimented a bit
here and there (like what happens if you dd over a complete PV to an existing
md device or vice versa or if you can keep the data if you create an md device
on a partition that already holds data), but I was able to keep all the data
and system during this.
Kai Schätzl, Berlin, Germany
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