[ENBD] joy

[greenail .]

I have a ENBD raid mirror that was running happily along for about 8
months until my service providor decided to reboot the boxen at around
2AM with no prior warning.  The heartbeat failover woked nicely but
i'm having a problem adding one of the 2 nbd devices back to the raid.
 I'm not sure if this is a enbd issue or not.  The other mirror hot
added fine, but was only 2G, the one that fails is 50G.

# mdadm  --force /dev/md0 -a /dev/ndc
mdadm: hot add failed for /dev/ndc: Invalid argument

DMSG:

Sep 16 16:15:46 186 kernel: md: trying to hot-add ndc to md0 ... 
Sep 16 16:15:46 186 kernel: md: error, md_import_device() returned -17

I googled but didn't find anything that helped... any ideas?