Once again with a -current i386 kernel, a disk on the
AdvanSys ASB-3940U2W [adw(4)] LVD chain has gone into
seisures and ended up triggering a bunch of these kernel
messages:

sd4(adw0:6:0): timed out
sd4(adw0:6:0): timed out
sd4(adw0:6:0): timed out
sd4(adw0:6:0): timed out

The disk is now wedged -- no accesses are working -- but
this time it's sd4 and not sd3 as usual.  (This is good,
since there are no binaries living on sd4, and swapctl -d
seems to work so nothing should hang).

sd3 is presently behaving perfectly.

Does anyone have some clues as to what could be going on?
The SCSI chain itself seems fine -- I can see uptimes of
days, with heavy use on both disks on the SCSI chain.  
envstat(8) reports nothing unusual.  A manual touch of
hot surfaces reveals nothing unusual.  

I'd love to have this fixed, because when it's sd3 that
fails, it hurts (the only fix I've found is to force a reboot).

        Sean.
- --
adw0 at pci0 dev 19 function 0: AdvanSys ASB-3940U2W SCSI adapter
adw0: interrupting at irq 10
scsibus2 at adw0: 16 targets, 8 luns per target
...
scsibus2: waiting 2 seconds for devices to settle...
sd3 at scsibus2 target 1 lun 0: <IBM, DGHS18D, 03E0> SCSI3 0/direct fixed
sd3: 17501 MB, 8154 cyl, 20 head, 219 sec, 512 bytes/sect x 35843670 sectors
sd4 at scsibus2 target 6 lun 0: <QUANTUM, QM318000TD-SW, N491> SCSI2 0/direct fi
xed
sd4: 17366 MB, 8057 cyl, 20 head, 220 sec, 512 bytes/sect x 35566500 sectors