Lots of errors in syslog from this device:
Jul 31 13:04:02 Tower kernel: sr 10:0:0:0: [sr0] tag#5 UNKNOWN(0x2003) Result: hostbyte=0x00 driverbyte=0x08
Jul 31 13:04:02 Tower kernel: sr 10:0:0:0: [sr0] tag#5 Sense Key : 0x5 [current]
Jul 31 13:04:02 Tower kernel: sr 10:0:0:0: [sr0] tag#5 ASC=0x64 ASCQ=0x0
Jul 31 13:04:02 Tower kernel: sr 10:0:0:0: [sr0] tag#5 CDB: opcode=0x28 28 00 00 00 00 01 00 00 01 00
Jul 31 13:04:02 Tower kernel: print_req_error: I/O error, dev sr0, sector 4
Any idea what that's about? I don't think it is a disk.
SMART for disk2 looks OK, but it is showing as still disabled in those diagnostics. They are a few days old though. You said you rebuilt?
Also those diagnostics are with the array not started, so there are some things they don't tell us, but nothing related to your question.