Too Busy For Words - the PaulWay Blog

Wed 8th Nov, 2006

Progress at last

In the long, complicated and frustrating quest to actually upgrade my MythTV machine to Fedora Core 6, and in the process get rid of the 40GB drive which holds its operating system, I think I've finally begun to make progress.

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[1] that spans two of the disks. Then, with a suitable mantra[2], you can copy the files across and set it up to boot from the new partition[3].

<voice style="bullwinkle">This time for sure!</voice>

[1]: 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.

[2]: 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 )'

[3]: 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.

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