ZFS zvol write speed incredibly slow

[Reed Wilson]

Hi guys!

I just got 7.0-RELEASE installed and running on my home server, and I've 
noticed incredibly slow write speeds to a ZFS zvol. Reading speeds seem 
normal. It may be related to the OpenSolaris bug #6428639:
http://bugs.opensolaris.org/view_bug.do?bug_id=6428639

 >> To another zpool:
# dd if=junk of=/tank2/junk bs=65536
1024+0 records in
1024+0 records out
67108864 bytes transferred in 0.331802 secs (202255676 bytes/sec)

 >> To a zvol in the same pool:
dd if=junk of=/dev/zvol/tank/tempvol bs=65536
1024+0 records in
1024+0 records out
67108864 bytes transferred in 11.575167 secs (5797658 bytes/sec)

Using smaller block sizes exacerbates the problem (444606 bytes/sec with 
4096-byte blocks!)

-- Reed