I have just set up an HP Micro Server N40L as a FreeNAS with 4 2tb drives in a RAIDZ. I am getting around 30-40MB/sec, with occasional bursts of 50MB/sec., reads and writes that are similar to the low end of that range. As far as I can tell the CPU is not overworked and when I did a file copy internally from one folder in the RAIDZ to another, I hit over 80MB/sec.
I am wondering what might be the best approach to improving read and write speeds. Tweaking my GigE network, adding a ZFS cache drive, etc.?