I have an Ubuntu (9.10) machine with 4 SATA disks. Each disk is partitioned identically, with the first few gigabytes set aside for a RAID 1 array (/dev/md0) for the boot volume, and the remainder set aside for RAID 5 (/dev/md1).

Recently, I upgraded to larger drives by repeatedly failing and removing a drive, replacing it with the larger one, partitioning it, and rebuilding onto it, per the instructions here. This all completed successfully.

However, the first time I reboot after upgrading, Ubuntu kicks me out to an initfs shell, claiming it can't find the root device. On checking /proc/mdstat, I discover that it's somehow assembled the entire drives (/dev/sda, /dev/sdb etc) into a single RAID 5 volume under /dev/md1, instead of assembling the partitions into their own arrays. Doing mdadm --stop /dev/md1; mdadm --assemble --scan fixes it, and both volumes are assembled correctly (and mount without issues).

What's going wrong, and how can I fix it?

1 Answer 1


Make sure you have /etc/mdadm.conf with proper configuration for your array. Even though Linux kernel can detect and assemble mdadm arrays automatically, sometimes it does funny things. Having /etc/mdadm.conf eliminates the uncertainty. Here is how mine looks like:

DEVICE  /dev/sdb /dev/sdc
ARRAY   /dev/md0 metadata=0.90 UUID=b8fdfd55:524cecb2:2d164f4f:84bee133

The ARRAY line comes from output of this command:

mdadm --examine --scan

Hope this helps.

  • Since it's halting in the initrd, I presume this isn't going to be able to read the updates if I just modify the files. Is there something I can do to have the updated mdadm.conf reflected in the initrd, other than editing it by hand? Jun 5, 2011 at 11:53
  • Doing as you suggested (only the devices line needed updating) worked, after running sudo update-initramfs -u. Thanks! Jun 5, 2011 at 12:01
  • Good job. I haven't been using it with boot devices, so you taught me something new :-)
    – dtoubelis
    Sep 27, 2011 at 0:52

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.