Hmm appears I've lost three drives and they happen to be on that one RAID6

Thanks for pointing me in the right direction.


Raid Level : raid6
Device Size : 488386496 (465.76 GiB 500.11 GB)
Array Size : 11721275904 (11178.28 GiB 12002.59 GB)
Raid Devices : 26
Total Devices : 25
Preferred Minor : 0

Update Time : Wed Oct 2 05:31:11 2013
State : active
Active Devices : 23
Working Devices : 24
Failed Devices : 3
Spare Devices : 1
Checksum : db8276a3 - correct
Events : 0.186898

Chunk Size : 64K