Bug#375879: fails to prepare initramfs if root is on LVM on RAID

[Neil Brown]

On Wednesday June 28, madduck at debian.org wrote:
> Package: mdadm
> Version: 2.5.2-1
> Severity: important
> 
> If rootfs is on LVM, which in turn is on RAID, the mdadm hook
> determines that RAID is not needed:
> 
>   ++ df /
>   ++ sed -ne 's,^\(/dev/[^[:space:]]\+\).*,\1,p'
>   + ROOTRAIDDEV=/dev/mapper/r1vg-root
>   + '[' -n /dev/mapper/r1vg-root ']'
>   + touch /tmp/mkinitramfs_yc5768/conf/mdadm.conf
>   + echo ROOTRAIDDEV=/dev/mapper/r1vg-root
>   ++ mdadm --detail /dev/mapper/r1vg-root
>   ++ sed -ne 's,[[:space:]]*UUID : ,,p'
>   + ROOTUUID=
>   + case "$ROOTUUID" in
>   + logger -sp syslog.notice -- 'I: mdadm: rootfs not on RAID, not including RAID stuff
> 
> This means we have to get rid of the optimisation in the initramfs
> and install all kernel modules, as before, and then tell mdadm to
> assemble *all* arrays from the initramfs. This sucks because it
> basically makes /etc/mdadm/mdadm.conf obsolete, unless the user will
> start and stop arrays on the running system.

mdadm.conf is not completely obsolete.  It can still contain useful
guidance for --monitor (such as expected number of spares).

Maybe you just need to be more subtle in tracing the structure of the
root device, though I agree that might be fairly complicated.

NeilBrown