ZFS & USB disks?

[James R. Van Artsdalen]

uname -a:
FreeBSD bigtex.housenet.jrv 8.0-CURRENT FreeBSD 8.0-CURRENT #0 r189099:
Fri Feb 27 07:09:47 CST 2009
james at bigtex.housenet.jrv:/usr/obj/usr/src/sys/GENERIC  amd64

This build is from before the recent USB changes.

Is it safe to use ZFS with USB disk drives?  The kernel output suggests
"SYNCHRONIZE_CACHE" isn't supported.  Does this cause a write-ordering
problem for ZFS?

Upon attaching a drive with a pool created on a Mac:

kernel: vdev_geom_attach:112[1]: Attaching to da4.
kernel: vdev_geom_attach:153[1]: Created consumer for da4.
kernel: (da4:umass-sim0:0:0:1): SYNCHRONIZE CACHE(10). CDB: 35 0 0 0 0 0
0 0 0 0
kernel: (da4:umass-sim0:0:0:1): CAM Status: SCSI Status Error
kernel: (da4:umass-sim0:0:0:1): SCSI Status: Check Condition
kernel: (da4:umass-sim0:0:0:1): ILLEGAL REQUEST asc:20,0
kernel: (da4:umass-sim0:0:0:1): Invalid command operation code
kernel: (da4:umass-sim0:0:0:1): (da4:umass-sim0:0:0:1): SYNCHRONIZE
CACHE(10). CDB: 35 0 0 0 0 0 0 0 0 0
kernel: (da4:umass-sim0:0:0:1): ILLEGAL REQUEST asc:20,0
kernel: (da4:umass-sim0:0:0:1): Invalid command operation code
kernel: Unretryable error
kernel: (da4:umass-sim0:0:0:1): error 22
kernel: (da4:umass-sim0:0:0:1): Unretryable Error