There's a problem with one of them since early booting :
Nov 19 22:03:25 cLNASty kernel: sd 6:0:11:0: [sdn] tag#0 UNKNOWN(0x2003) Result: hostbyte=0x0b driverbyte=0x00
Nov 19 22:03:25 cLNASty kernel: sd 6:0:11:0: [sdn] tag#0 CDB: opcode=0x88 88 00 00 00 00 03 a3 81 2a a8 00 00 00 08 00 00
Nov 19 22:03:25 cLNASty kernel: print_req_error: I/O error, dev sdn, sector 15628053160
Nov 19 22:03:25 cLNASty kernel: sd 6:0:11:0: [sdn] tag#1 UNKNOWN(0x2003) Result: hostbyte=0x00 driverbyte=0x08
Nov 19 22:03:25 cLNASty kernel: sd 6:0:11:0: [sdn] tag#1 Sense Key : 0x2 [current]
Nov 19 22:03:25 cLNASty kernel: sd 6:0:11:0: [sdn] tag#1 ASC=0x4 ASCQ=0x0
Nov 19 22:03:25 cLNASty kernel: sd 6:0:11:0: [sdn] tag#1 CDB: opcode=0x88 88 00 00 00 00 03 a3 81 2a a8 00 00 00 08 00 00
Nov 19 22:03:25 cLNASty kernel: print_req_error: I/O error, dev sdn, sector 15628053160
Check connections, there's not even a valid SMART report.