Do I have to worry about "error: superfluous RAID member"?

Solution 1:

As mentioned here by Fussy Salsify this seems to be a bug of update-grub script with spare device in one of the RAID arrays. As mentioned here a patch has been applied and should come to Ubuntu at some time.

Boyd Stephen Smith Jr. said he thinks this error report may be just cosmetic here and Vladimir 'φ-coder/phcoder' Serbinenko submitted a patch that seems to just change the error report to "spares aren't implemented".

Also there is a bug report at launchpad (#816475) and a possible workaround that involves changing the partitioning. The importance of this bug is undecided at launchpad but looks like it caused some real problem to Björn Tillenius that could not upgrade/install grub. So looks like you should be careful.

Solution 2:

I was getting this error on ubuntu 12.04 both during upgrade-grub and briefly upon booting the PC but it was due to a misconfiguration on my side:

I had two partitions on two disks paired with mdadm using RAID1. After one disk crashed I replaced it and added a new one but at some point while entering the commands to add the partitions (mdadm --manage /dev/md... -a /dev/sd...) I erroneously added the whole disk (/dev/sdb) instead of the partition (/dev/sdb1) as part of /dev/md1. I removed the whole disk and correctly added the partition and things were looking just fine at /proc/mdstat so I thought I was over.

However upon rebooting "error: superfluous RAID member (2 found)." was appearing briefly on my screen and the raid array was not reconstructed with my the partitions of the new disk.

I had to zero-out the superblock of /dev/sdb (the disk) with mdadm --zero-superblock /dev/sdb to fix it which also got rig of the "error: superfluous RAID member (2 found)." both from startup and update-grub.