maybe check out this:
http://techreport.com/discussions.x/13849I have built my own Solaris/OpenSolaris server machines and did some research on the x4500 before it was EOL. Browsing some of the documentation on oracle.com makes me think the drives mate with the I/O board and controllers are part of the I/O board. I've just read in Sun documentation that the controllers are LSI, but also seen Marvell driver download links and the above article has a diagram showing the Marvell controllers.
Here's the thing, that machine was intended to use ZFS. It was intended to use lots of cheap SATA drives. I don't think you'll be able to use SAS drives, or dedicated RAID controllers. Just not what the machine was designed to do. You might be able to use Linux if you don't like Solaris, but I'd say ZFS is a better solution than LVM and software RAID on Linux.
Not sure what Bri3d means about reliability with ZFS. I've read a lot of success stories and haven't had an issue with my own couple TBs. It's not fair to compare RAID-6 with RAIDZ, RAIDZ2 would be comparable. Speed? Well if you want speed you don't use RAID-5/RAID-6 or similar.
Stripes across mirrored pairs would be better in this application. It's expandable, fast and offers better rebuild times.
I am not a fan of dedicated controllers. The Opterons in the X4500 are faster than the little CPU on a RAID card. If you look at how most Filers and other storage appliances work, they don't use RAID cards either. A NetApp for example is really just a custom PC with custom software, FC ports and a bunch of JBODs.
My own RAIDZ arrays have been stable and fast enough running on slow Core2Duo based Pentiums.