Write Timeouts with MPS

[John Hickey]

I've seen people having this problem before, but I don't think anyone
has figured it out.  I am running:

FreeBSD zfs 10.0-CURRENT FreeBSD 10.0-CURRENT #5: Sat Apr  7 18:05:57 PDT 2012     root at zfs:/usr/obj/usr/src/sys/GENERIC  amd64

I have the latest LSI IT firmware 13 loaded:

mps1: <LSI SAS2008> port 0xc000-0xc0ff mem 0xfe93c000-0xfe93ffff,0xfe940000-0xfe97ffff irq 16 at device 0.0 on pci5
mps1: Firmware: 13.00.01.00, Driver: 13.00.00.00-fbsd
mps1: IOCCapabilities: 1285c<ScsiTaskFull,DiagTrace,SnapBuf,EEDP,TransRetry,EventReplay,HostDisc>

All disks are on a SuperMicro SAS II backplane:

root at zfs:/usr/ports/sysutils/dmidecode# camcontrol devlist
<SEAGATE ST3300657SS 0008>         at scbus0 target 0 lun 0 (da0,pass0)
<SEAGATE ST3300657SS 0008>         at scbus0 target 1 lun 0 (da1,pass1)
<SEAGATE ST2000NM0001 0001>        at scbus1 target 8 lun 0 (da2,pass2)
.... x16 more of the same
<SEAGATE ST2000NM0001 0001>        at scbus1 target 46 lun 0 (da20,pass20)
<LSI CORP SAS2X36 0717>            at scbus1 target 47 lun 0 (ses0,pass21)

Essentially when putting the ZFS filesystem under load, I am getting
these sorts of errors:

(da13:mps1:0:21:0): WRITE(10). CDB: 2a 0 19 29 32 f2 0 1 0 0 length 131072 SMID 213 terminated ioc 804b scsi 0 state c xfer 0
(da7:mps1:0:13:0): WRITE(10). CDB: 2a 0 19 3d fa ae 0 1 0 0 length 131072 SMID 386 terminated ioc 804b scsi 0 state c xfer 0
(da11:mps1:0:18:0): WRITE(10). CDB: 2a 0 18 a 24 ee 0 1 0 0 length 131072 SMID 542 terminated ioc 804b scsi 0 state c xfer 0
(da14:mps1:0:22:0): WRITE(10). CDB: 2a 0 19 2a c6 b1 0 1 0 0 length 131072 SMID 214 terminated ioc 804b scsi 0 state c xfer 0
(da16:mps1:0:25:0): WRITE(10). CDB: 2a 0 19 2b 83 aa 0 1 0 0 length 131072 SMID 879 terminated ioc 804b scsi 0 state c xfer 0
(da7:mps1:0:13:0): WRITE(10). CDB: 2a 0 19 40 d f9 0 1 0 0 length 131072 SMID 474 terminated ioc 804b scsi 0 state c xfer 0
(da9:mps1:0:15:0): WRITE(10). CDB: 2a 0 18 c 3 31 0 1 0 0 length 131072 SMID 578 terminated ioc 804b scsi 0 state c xfer 0
(da4:mps1:0:10:0): WRITE(10). CDB: 2a 0 19 41 6f ff 0 1 0 0 length 131072 SMID 703 terminated ioc 804b scsi 0 state c xfer 0
(da12:mps1:0:19:0): WRITE(10). CDB: 2a 0 18 c e5 2e 0 1 0 0 length 131072 SMID 684 terminated ioc 804b scsi 0 state c xfer 0
(da3:mps1:0:9:0): WRITE(10). CDB: 2a 0 19 41 b1 4b 0 1 0 0 length 131072 SMID 212 terminated ioc 804b scsi 0 state c xfer 0
(da9:mps1:0:15:0): WRITE(10). CDB: 2a 0 18 d 1e 5c 0 1 0 0 length 131072 SMID 63 terminated ioc 804b scsi 0 state c xfer 0
(da11:mps1:0:18:0): WRITE(10). CDB: 2a 0 18 d 56 1c 0 1 0 0 length 131072 SMID 412 terminated ioc 804b scsi 0 state c xfer 0
(da4:mps1:0:10:0): WRITE(10). CDB: 2a 0 19 42 2c f1 0 1 0 0 length 131072 SMID 1019 terminated ioc 804b scsi 0 state c xfer 0
(da11:mps1:0:18:0): WRITE(10). CDB: 2a 0 18 d 6d 22 0 1 0 0 length 131072 SMID 175 terminated ioc 804b scsi 0 state c xfer 0
(da7:mps1:0:13:0): WRITE(10). CDB: 2a 0 19 42 62 bc 0 1 0 0 length 131072 SMID 458 terminated ioc 804b scsi 0 state c xfer 0
(da10:mps1:0:16:0): WRITE(10). CDB: 2a 0 18 f 4b d2 0 1 0 0 length 131072 SMID 986 terminated ioc 804b scsi 0 state c xfer 0
(da3:mps1:0:9:0): WRITE(10). CDB: 2a 0 19 43 f4 50 0 1 0 0 length 131072 SMID 809 terminated ioc 804b scsi 0 state c xfer 0
(da2:mps1:0:8:0): WRITE(10). CDB: 2a 0 19 45 4 18 0 1 0 0 length 131072 SMID 998 terminated ioc 804b scsi 0 state c xfer 0
(da13:mps1:0:21:0): WRITE(10). CDB: 2a 0 19 30 e4 73 0 1 0 0 length 131072 SMID 489 terminated ioc 804b scsi 0 state c xfer 0
(da12:mps1:0:19:0): WRITE(10). CDB: 2a 0 18 10 8d 19 0 1 0 0 length 131072 SMID 275 terminated ioc 804b scsi 0 state c xfer 0
(da14:mps1:0:22:0): WRITE(10). CDB: 2a 0 19 32 e7 0 0 1 0 0 length 131072 SMID 666 terminated ioc 804b scsi 0 state c xfer 0
(da8:mps1:0:14:0): WRITE(10). CDB: 2a 0 18 13 2b 68 0 1 0 0 length 131072 SMID 463 terminated ioc 804b scsi 0 state c xfer 0