Thanks for the reply, but I'm not sure you understand. I swapped the disks in bays 3 & 4 as you suggested to see if there was a problem with one of the bays. Now the 2nd blue light isn't coming on for either drive. I've put them back again, and the phydrv command is showing this still:
cliib> phydrv
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PdId Model Type Capacity Location OpStatus ConfigStatus
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1 Hitachi HDS7 SATA HDD 1TB Encl1 Slot1 OK Array0 No.0
2 Hitachi HDS7 SATA HDD 1TB Encl1 Slot2 OK Array0 No.1
3 Hitachi HDS7 SATA HDD 1TB Encl1 Slot3 OK Array0 No.2
Lost Physical Drives
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PdId Model PhyCapacity Location OpStatus ConfigStatus
===============================================================================
4 ATA 0Byte Unknown Missing Array0 No.3
I've now repaced the drive in bay 4 with a new one. Is there a good example online that shows how to rebuild the array? I can't click 'rebuild' as the button isn't enabled: