I recently acquired an HP Z800 workstation that has five 300 GB 15K SAS Drives. This system will be dedicated to running multiple virtual machines under VMware Workstation (Note: I'm not using ESXi because I do plan to use the system for other purposes.). For the host OS, I plan to install RHEL 5. My number one concern is guest performance. For example, should I create a RAID 10 array for the OS and virtual machine storage with four of the drives and reserve the 5th? Or, is there a solution that will provide better performance?
I'd use a single disk for OS and code then R10 the remaining four to use for VM guest storage.
A simple JBOD will probably give you the best performance for most work on this type of machine unless your application is really database heavy. Small RAID-10 volumes are not necessarily all that much faster in practice than a JBOD with the I/O distributed over the disks. Unless you need the data integrity you probably won't get much of a gain.
If you want RAID you're probably best off with 4 drives in a RAID-10 and the fifth for either a system disk or a hot spare. On something the size of a Z800 the working set of the system should fit into the system disk cache, so a separate system disk might or might not significantly improve performance.
On a database heavy workload (I have some XW9300s that I use for data warehouse development machines) you would be better off with 6 disks (I use a 5.25"=3.5" mounting bracket in one of the 5.25" bays for this). I use a pair in a RAID-1 and 4 disks in a RAID-10 with a H/W RAID controller. I'm not sure if there are enough drive bays in a Z800 to do this. This configuration is quite fast (The RAID-10 is configured with a 256k stripe size) and I've had it significantly outperform SANs for ETL processing on a couple of occasions now.