I have a USB2 dock that accepts SATA drives. On Ubuntu 10.10, just writing raw data to the SATA disks results in just about 22-28MB/s streaming write. I used ‘dd if=/tmp/test_file_1G of=/dev/sdb bs=1M’. The first time I got around 22MB/s, then the source file was in the kernel’s disk cache, so on subsequent runs, the speed jumped up to ~28MB/s. Well below the almost ~70MB/s streaming write that the drive can do (according to other posts on the web).
Then I formatted the disk with ext2 and mounted it and tried copying that same source file there with rsync. The transfer speed was ~21-25MB/s over a bunch of iterations.