On 14/01/20 14:47, William Morgan wrote:

Well, I went ahead and tried the forced assembly:

bill@bill-desk:~$ sudo mdadm --assemble --force /dev/md1 /dev/sdg1
/dev/sdh1 /dev/sdi1
[sudo] password for bill:
mdadm: Merging with already-assembled /dev/md/1

This looks like your problem ... it looks like you have a failed
assembly active. Did you do an "mdadm --stop /dev/md1"? You should
always do that between every attempt.

mdadm: Marking array /dev/md/1 as 'clean'
mdadm: failed to RUN_ARRAY /dev/md/1: Input/output error

I hope that's a good sign - if it's got an array that doesn't make sense
then everything should have stopped at that point and the --force won't
have done any damage.

(The drive letters have changed because I removed a bunch of other
drives. The original drives are now on sd[b,c,d,e] and the copies are
on sd[f,g,h,i] with sdf being a copy of the presumably bad sdb with
the event count which doesn't agree with the other 3 disks.)

Make sure md1 doesn't appear to exist at all (--stop), and then try
again ...

Cheers,
Wol