Lego - FreeBSD
su-2.05b# dd if=/dev/ad2 of=FC-image.img bs=1k 
31296+0 records in
31296+0 records out
32047104 bytes transferred in 18.643573 secs (1718936 bytes/sec)
su-2.05b# dd if=FreeNAS-generic-pc-0.64.img of=/dev/ad2 bs=1k count=12336221
dd: /dev/ad2: Invalid argument
12047+1 records in
12047+0 records out
12336128 bytes transferred in 73.528462 secs (167774 bytes/sec)
Valeo - OSX
Valeo:~ gjb$ sudo dd bs=1k if=FreeNAS-generic-pc-0.64.img of=/dev/rdisk2
dd: /dev/rdisk2: Invalid argument
12039+1 records in
12039+0 records out
12327936 bytes transferred in 40.067269 secs (307681 bytes/sec)