The final realisation today was that, if I abandon my crazy idea to have a MD RAID5 on top of three LVM LVs, I have much more likelihood of success. Instead, I can configure a mirrored LV that spans two of the disks. Then, with a suitable mantra, you can copy the files across and set it up to boot from the new partition.
<voice style="bullwinkle">This time for sure!</voice>
: Creating a mirrored LV with only two disks is actually completely impossible with LVM, despite it seeming perfectly logical. This is because you need a further physical volume on which to store the log volume, which is automatically created by lvcreate and stores the write journal to keep the two mirrored volumes in sync.
: find / -mount -depth -print0 | cpio --null -apmuvd /new/mount/point. Or, if you're like me and want to leave it to do its job without clogging up your console, dtach -c ~/cpio-socket bash -c '( find / -mount -depth -print0 | cpio --null -apmuvd /new/mount/point )'
: You do this by changing the grub configuration file /boot/grub/grub.conf. Change the 'root=LABEL=/' text to be 'root=/dev/volumegroup/rootvolume'. Make sure that your new root's /etc/fstab lists itself correctly.
All posts licensed under the CC-BY-NC license. Author Paul Wayper.