When I make the _2nd_ access to /dev/rcd0c  (see relevant config/dmesg below),
the access hangs on wait channel scsipi or cdlck, and there is a console 
message:

ncr0: SCSI phase error fixup: CCB already dequeued (0xfffffe000004c000)
ncr0: timeout ccb=0xfffffe000004c000 (skip)

The drive access lights go on solid, and no access to cd0 works.

By not working, that means hanging or complaining about an i/o error.

Sometimes I get a console message when an access hangs:

ncr0: timeout ccb=0xfffffe000004d800 (skip)

Processes in scsipi are unkillable; processes in cdlck are killable.
ps l and DDB tracebacks below.

FWIW, the _1st_ access after reboot works OK, notwithstanding type of access.

	Sean.

options FAILSAFE # from ncr(4) on alpha.  doesn't seem to make any difference.
isp*    at      pci? dev ? function ?           # Qlogic ISP 10x0 SCSI
ncr*    at      pci? dev ? function ?           # NCR 53c8xx SCSI
scsibus0 at     isp?
scsibus1 at     ncr?

ncr0 at pci0 dev 6 function 0: ncr 53c810 fast10 scsi
ncr0: interrupting at isa irq 11
ncr0: minsync=25, maxsync=206, maxoffs=8, 16 dwords burst, normal dma fifo
ncr0: single-ended, open drain IRQ driver
ncr0: restart (scsi reset).
...
scsibus1 at ncr0: 8 targets, 8 luns per target
scsibus1: waiting 2 seconds for devices to settle...
cd0 at scsibus1 targ 0 lun 0: <TEAC, CD-R55S, 1.0K> SCSI2 5/cdrom removable
probe(ncr0:0:1): asynchronous.

- --
  UID   PID  PPID CPU PRI NI   VSZ  RSS WCHAN  STAT TT       TIME COMMAND
    0   798   769   0  -6  0   408  168 cdlck  S    p5    0:00.01 disklabel cd0
db> t/t 31e
trace: pid 798 at 0xfffffe0006f53ae8
mi_switch() at mi_switch+0x188
tsleep() at tsleep+0x2f0
cdopen() at cdopen+0xd0
spec_open() at spec_open+0x1dc
vn_open() at vn_open+0x440
sys_open() at sys_open+0xf0
syscall() at syscall+0x1d4
XentSys() at XentSys+0x50
--- syscall (5, netbsd.sys_open) ---
--- user mode ---

alfa# ps l561
  UID   PID  PPID CPU PRI NI   VSZ  RSS WCHAN  STAT TT       TIME COMMAND
    0   561   531   0  -5  0   408  168 scsipi D+   p0    0:00.01 disklabel cd0
db> t/t 231
trace: pid 561 at 0xfffffe0006f27a28
mi_switch() at mi_switch+0x188
tsleep() at tsleep+0x2f0
scsipi_execute_xs() at scsipi_execute_xs+0x108
scsi_scsipi_cmd() at scsi_scsipi_cmd+0x1d4
scsipi_test_unit_ready() at scsipi_test_unit_ready+0x60
cdopen() at cdopen+0x144
spec_open() at spec_open+0x1dc
vn_open() at vn_open+0x440
sys_open() at sys_open+0xf0
syscall() at syscall+0x1d4
XentSys() at XentSys+0x50
--- syscall (5, netbsd.sys_open) ---
--- user mode ---