On Sat, 15 Feb 2014, Jon Nelson wrote:

Out of 12 drives, I thought RAID6 only offered a total of *2* failed 
devices. It seems to me that you have 7 devices in sync and 4 *almost* 
in sync. It's this "almost" part that has me confused. How can the raid 
run if the event count doesn't match? Wouldn't at least 10 out of 12 
drives have to have the same event count to avoid data loss?

Correct. When you use --assemble --force you're basically telling mdadm "I 
know what I'm doing and I'll take the risk of data loss or corruption". If 
you assemble in with a kicked drive that was kicked long ago that has a 
really far off event count, you can really really screw things up.

Unless you use --force, mdadm won't assemble an array where the event 
count doesn't match up.

-- 
Mikael Abrahamsson    email: swmike@swm.pp.se