I did a minor booboo with my mdadm raid6. I suspended (not shutdown, but
suspend-to-ram) the machine to install a *new* disk in a hotswap bay for
a thorough test before usage. This machine also housed a mdadm raid6
array with 4 disks /dev/sd[cdeg]1 (not /dev/sdf1). When I inserted the
new disk, I also rearranged the disks in the hotswap cage. I think that
is a stupid mistake because /dev/sdg1 was also in the cage and now
became /dev/sdf1 and the new disk got the name /dev/sdg1. I did not
think much about it, since I thought mdadm would assemble after a resume
and will find the right disks. I did not bother to check if anything
happened to /dev/md0.
After checking the new disk (now /dev/sdg1) I added /dev/sdg1 to md0 (as
spare) without checking /proc/mdstat. I noticed rebuild started to my
surprise. I was trying to figure out what happened. It looks like resume
after suspend does not assemble md0 as it does for reboot. So, it looked
at the new /dev/sdg1 and found to be not part of md0 and degraded the
array. So when I added it, it thought I am adding a new drive and
proceeded to rebuild to fix the degraded state. A quick check of
/dev/sdf1 (which was /dev/sdg1 before my swap) contains everything
right, but got kicked out of array due to suspend-swap disk-resume issue.
While this is not a disaster, I wonder if my understanding is correct?
Does this mean mdadm does not scan to assemble as part of resume? More
importantly, how should I rectify the situation like this? Reboot or
simply stop md0 and scan in a live system?
Further, how do I use /dev/sdf1 (that was /dev/sdg1 before this
problem)? zero-superblock and add back to md0?
Sorry, if this was already discussed. If so, just let me know and I will
search the archive manually as Google did not find it.
Thanks for your help
Ramesh
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