initramfs' init-premount degrades *all* arrays (not just those required to boot)

[ceg]

After a timeout mdadm in initrams degrades all arrays instead of just those required for the rootfs.

This is not good since non-rootfs arrays are likely to be available only incompletely (due to the early stage during boot) and are getting desynced by this.

When creating the initramfs image the mdadm hook should determine the dependencies of the rootfilesystem and save a list of the required md devices in the initramfs.

See: How would you decide what device is needed? at https://wiki.ubuntu.com/ReliableRaid

Currently the initramfs boot script just looks for *any* available incomplete array and calls "mdadm --assemble --scan --run", which will start *all* runnable arrays.

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comment #2 contains a workaround for the proper command to run single arrays degraded.

[ceg (ceg)]

On https://wiki.ubuntu.com/ReliableRaid See: How would you decide what device is needed?

Only raids required for the rootfs should be started degraded if they haven't come up for a while.

(Within the ubuntu hotplug-scheme /usr/share/initramfs-tools/hooks/cryptroot contains code that may be usefull to determine devices that the fstab depends on.)

[ceg (ceg)]

As long as the proper mdadm --incremental mode command (to start a single array) is not available (Bug #251646) a workaround needs to be used:

mdadm --remove <incomplete-md-device> <arbitrary-member-device-of-incomplete-array>

mdadm --incremental --run <arbitrary-member-device-of-incomplete-array>

[ceg (ceg)]

Note that with the UUID-based raid assembly
https://bugs.launchpad.net/ubuntu/+source/mdadm/+bug/158918/comments/33
the mdadm.conf file is not used to store ARRAY definitions any more.

Thus the (UUID) list of raid devices required to mount the rootfs must be stored in a separate file within initramfs.

[Dustin Kirkland  (kirkland)]

@ceg-

I read through https://wiki.ubuntu.com/ReliableRaid, and it looks pretty good. Are you willing to implement this for Maverick?

[ceg (ceg)]

Hi Dustin, I am not a developer and don't know how to create packages etc. Though, I have gathered information from using mdadm and bugreports to make it easier for a developer to bring ubuntu's mdadm setup in shape.