>   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?
increase blocksize.