Well 3 of the 4 are 7200 RPM disks. One is a new WD, one of the green ones, but that's not the one I benchmarked. And I know the 3 7200s should be at least as fast as the disk that's in the desktop, but they aren't even close. Anyway, 4MB/sec would be pathetic for a modern disk, if that's all it could manage.
I would understand more if I had a bunch of RAID overhead, but since I'm not doing that I'm a little surprised that it's as slow as it is. It's got me contemplating building a WHS machine or putting a file server together again, which is unfortunate, as I wanted a NAS to get away from running a full blown server, but the slow performance is starting to bother me.