Ok i tried what you suggested and found the following
dd if=/dev/zero of=/mnt/esata/test bs=1M count=256
256+0 records in
256+0 records out
268435456 bytes (268 MB) copied, 34.1654 s, 7.9 MB/s
bad!!
Good to see you got your problem worked out. Just for curiosity's sake, I tried the same test on my 2TB USB connected external HDD, here's what I got:
una@sheeva:~$ dd if=/dev/zero of=/mnt/monster/test bs=1M count=256
256+0 records in
256+0 records out
268435456 bytes (268 MB) copied, 8.86686 s, 30.3 MB/s
Not too bad for USB, I imagine. Mine is set to async.