Dead Disk.. but not really

You had batter not use ST2000DL003, Seagate drive has "FLUSH CACHE EXT" hang problem, the symptom would be exactly same as described:
Entire disk(all partitions) not responding, only power cycle can bring it back.
Seagate recently admitted this issue, they have a test firmware to address this hang issue.
Please check kernel.log and find if it has "FLUSH CACHE EXT", please see below information,

Apr 15 16:36:59 Orac kernel: TCP: Possible SYN flooding on port 36130. Sending cookies.
Apr 17 00:52:35 Orac kernel: ata2.00: exception Emask 0x0 SAct 0x0 SErr 0x0 action 0x6 frozen
Apr 17 00:53:36 Orac kernel: ata2.00: failed command: FLUSH CACHE EXT
Apr 17 00:53:36 Orac kernel: ata2.00: cmd ea/00:00:00:00:00/00:00:00:00:00/a0 tag 0
Apr 17 00:53:36 Orac kernel: res 40/00:01:00:4f:c2/00:00:00:00:00/00 Emask 0x4 (timeout)
Apr 17 00:53:36 Orac kernel: ata2.00: status: { DRDY }
Apr 17 00:53:36 Orac kernel: ata2: hard resetting link
Apr 17 00:53:36 Orac kernel: ata2: link is slow to respond, please be patient (ready=0)
Apr 17 00:53:36 Orac kernel: ata2: COMRESET failed (errno=-16)
Apr 17 00:53:36 Orac kernel: ata2: hard resetting link
Apr 17 00:53:36 Orac kernel: ata2: link is slow to respond, please be patient (ready=0)
Apr 17 00:53:36 Orac kernel: ata2: COMRESET failed (errno=-16)
Apr 17 00:53:36 Orac kernel: ata2: hard resetting link
Apr 17 00:53:36 Orac kernel: ata2: link is slow to respond, please be patient (ready=0)
Apr 17 00:53:36 Orac kernel: ata2: COMRESET failed (errno=-16)
Apr 17 00:53:36 Orac kernel: ata2: limiting SATA link speed to 1.5 Gbps
Apr 17 00:53:36 Orac kernel: ata2: hard resetting link
Apr 17 00:53:36 Orac kernel: ata2: COMRESET failed (errno=-16)
Apr 17 00:53:36 Orac kernel: ata2: reset failed, giving up
Apr 17 00:53:36 Orac kernel: ata2.00: disabled
Apr 17 00:53:36 Orac kernel: ata2.00: device reported invalid CHS sector 0
Apr 17 00:53:36 Orac kernel: ata2: EH complete
Apr 17 00:53:36 Orac kernel: sd 1:0:0:0: [sdb] Unhandled error code
Apr 17 00:53:36 Orac kernel: sd 1:0:0:0: [sdb] Result: hostbyte=DID_BAD_TARGET driverbyte=DRIVER_OK
Apr 17 00:53:36 Orac kernel: sd 1:0:0:0: [sdb] CDB: Read(10): 28 00 00 30 c2 e0 00 00 08 00
Apr 17 00:53:36 Orac kernel: end_request: I/O error, dev sdb, sector 3195616
Apr 17 00:53:36 Orac kernel: md/raid1:md0: sdb1: rescheduling sector 3195528
Apr 17 00:53:36 Orac kernel: sd 1:0:0:0: [sdb] Unhandled error code
Apr 17 00:53:36 Orac kernel: sd 1:0:0:0: [sdb] Result: hostbyte=DID_BAD_TARGET driverbyte=DRIVER_OK
Apr 17 00:53:36 Orac kernel: sd 1:0:0:0: [sdb] CDB: Read(10): 28 00 00 32 42 50 00 00 08 00
Apr 17 00:53:36 Orac kernel: end_request: I/O error, dev sdb, sector 3293776
Apr 17 00:53:36 Orac kernel: md/raid1:md0: sdb1: rescheduling sector 3293688