I recently had a need for a SATA RAID card that worked with Linux, so I opted for the LSI MegaRaid 8204XLP based on their advertisement of Linux support including SLES 9 and 10 along with RHEL 4 and 5. Actually, I originally went with an Adaptec 1420SA which was an unmitigated disaster, but that is the topic of a different discussion. My first step with the LSI card was CentOS 5.2 and Anaconda was able to successfully load the drivers and recognize the array, but that is where the fun stopped. On restart, initrd crashed when trying to load the kernel and hung. I contacted LSI support with the issue and they were diligent but it became immediately clear that their level 2 support techs new far less about this problem than I already did. I tested the issue with a number of other RHEL kernels including a 4.7 kernel and all had the same issue. I also discovered that the issue only occurred if the drives were plugged into the card and when unplugged, the server would boot correctly (aside from fstab errors associated with a missing volume. Eventually I gave up on Red Hat/CentOS altogether and gave it a shot with SuSe Enterprise Server 10.2 with the SLES drivers downloaded from LSI and it worked like a charm.
Overall, I was eventually able to make the 8204XLP work and there are apparently a significant number of people out there who have had success with RHEL. Once working, the performance seems quite solid although I have not benchmarked it. However, the Linux support from LSI is less than inspirational, both in terms of drivers and technical support and I would recommend caution when buying this card for use with Linux.