Parallels Server For Mac configuration (or any VM product), best practices

What is the recommended practice for configuring Parallels Server For Mac on an XServe? The xserve has 3 hard drive bays. What do most people do to maximize uptime, failover, disaster recovery, etc. We do have 3 different physical xserves with PSfM also.

Is a software RAID recommended for the boot OS drive? for the drive storing the VMs if not the same drive?

How are your hard drives configured?

I'm concerned that mirroring two 1TB hard drives and using that for both the host OS and for the VMs will present problems:

When creating new VMs, copying large amounts of data, etc, I'd guess that moving 10-100 GB of data is tasking for the software raid and will noticeably affect performance for all VMs.

If one of the mirrored drives fails and the raid needs to be rebuilt, this probably would bring the entire system to a crawl, at best, and possibly be unusable while it works to repair the raid. Thus it would have to be done during off peak hours. This would prevent a complete outage though.

are these correct assumptions?