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