I have recently been trying to install Linux to a Compaq DL380 G3 server. It's got an onboard RAID controller, so I populated it with 4 disks, set RAID5, with online spare, in the controller BIOS, and made one logical drive. So far, so good.
Any version of Linux I tried that was recent (OpenSuSE 10.2, Mandriva 2007, FC6), would die when it tried to do anything with the disk. Either the drive wouldn't be found, or it couldn't load the driver for the controller, or said there was no disk there at ALL. Even going to a single hard drive didn't work, but loading an older verion of OpenSuSE (10.0), worked. Hmmm...
The solution was go to to the HP site here: http://h18004.www1.hp.com/support/fi...oad/27095.html
, and download the support pack. It supports a bunch of HP/Compaq servers, and is an ISO image. Burn it to CD, boot from it, and upgrade the system firmware and BIOS. After that, I had no problems at all loading, either single-drive or RAID5. This particular link says it's for OpenSuSE, but since this just affects the BIOS and firmware, it (should) be ok for any other Linux distro. YMMV, and please read the docs.