I am trying to transfer data from a memory filesystem (mounted on /mnt) to
raw disk device at a certain offset.

When I try:
  dd if=/mnt/pre of=/dev/wd0g count=20480 skip=0 seek=0
I get
  10485760 bytes transferred in 30 secs (349525 bytes per sec)

When I change '/dev/wd0g' to '/dev/rwd0g':
  dd if=/mnt/pre of=/dev/wd0g count=20480 skip=0 seek=0
I get
  10485760 bytes transferred in 7 secs (1497965 bytes per sec)

This shows that dd'ing to rwd0g is remarkably faster than wd0g. However,
1497965 bytes per sec still seems slow. If I write to a file in /usr/tmp
(which is /usr/wd0e mount_ffs'ed):
  dd if=/mnt/pre of=/usr/tmp/TEST count=20480 skip=0 seek=0
I get
  10485760 bytes transferred in 1 secs (10485760 bytes per sec)

Does this make sense? Can anybody tell me how I can very quickly transfer
this sort of volume of data to a raw disk device at a high speed?

Many thanks
 Bruce Martin