Re: RAID-6 mdadm disks out of sync issue (more questions)

[<linux-raid.vger.kernel.org@atu.cjb.net>]

So here I was thinking everything was fine.  My six disks were working
for hours and the other two disks were loaded as spares and the first
one was rebuilding, up to 30% with an ETA of 5 hours.  I left the house
for a few hours and when I came back, the same disk with read errors
before had spontaneously disconnected and reconnected three times (I
saw in dmesg).  It probably got around 80% of the way through the six
hour rebuild.

The problem is that when the /dev/sdc disk reconnected itself after,
it was marked as a "Spare", and now I can't use the same command any
longer:

# mdadm --assemble /dev/md13 --verbose --force /dev/sd{a,b,c,d,e,f}1

This time it doesn't work, as it says 5 disks and 1 spare isn't enough
to start the array.  I also tried --re-add, but it already thinks it
is disk 9 out of 8, a Spare.

How can I safely put this disk back into its proper place so I can
again try to rebuild disks 7 and 8?  I'm assuming I probably need to
use mdadm --create, but I'm not sure, and don't want to get it wrong
and have it overwrite this needed disk.

 - S.A.