It depends on what you are planning on using the server for as to whether you actually need a hardware raid controller. If this is a personal server, I would suggest using the raid mdadm raid functionality built into the Linux kernel. I have heard that it many cases it is actually more reliable than cheap raid controllers. In fact, I have used it for a couple years on Debian Squeeze with no problems at all. I have also had no issues since upgrading the machine in question to Debian Wheezy once it went into release freeze. There is a good tutorial here
for setting up raid 1.Edit:
Upgrading from a pair of 320 GB disks to a pair of 750 GB disks was no problem at all. I have found mdadm very well documented and fairly easy to use. However, if you are interested in going the BSD route, ZFS is also very well documented in the FreeBSD manual and can do even more cool things than just mdadm+EXT4 since it combines the file system and volume manager.Edit 2:
As a heavy Debian user, I feel compelled to mention that Debian has a FreeBSD port
. According to the official project page, "Debian GNU/kFreeBSD is a port that consists of GNU userland using the GNU C library on top of FreeBSD's kernel, coupled with the regular Debian package set." If you go with Debian, whether it be kFreeBSD-AMD64 or simply the Linux-based AMD64 release, I recommend that you download the latest Wheezy beta installer
since Squeeze will be replaced soon and Wheezy is already quite stable.