[CentOS] Reassemble software RAID

Scott Silva ssilva at sgvwater.com
Tue Dec 2 23:58:14 UTC 2008

on 12-2-2008 10:31 AM Kai Schaetzl spake the following:
> 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
As long as your system is back up, then no worries!

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