Server with 3 Disk, what's the best HD Configuration?

I Have an HP Server with a quad core Opteron and 3 Disk 250Gb S-ATA Disk, i'm thinking about what's the best configuration of the disk for performance and reliability.

There is mainly 2 scenario : -RAID 5 with these 3 HD (on the the array 100GB Partition for OS, Other Space for Data Partition) -RAID 1 + 1 Disk for OS (one single Disk OS Installation, RAID 1 Array for a Data Partition)

What's the best configuration ?

In the Server Run MySQL and Small Document File server, the OS to be installed is Windows Server 2008 ...

Best option is to buy a 4th disk and R10 them.

RAID5 can be a little dangerous if you do not have a hot spare. If one drive fails, you'll need to replace it quickly, so that you don't risk a double-drive failure. Also during the failure, a RAID5 array will be noticeably slower.

I like to do RAID1 + 1 hot spare, which usually does well for mid and low-range servers (web servers, app servers, small MySQL database servers).

If your hardware RAID controller supports something like what IBM call RAID1E (Linux can do something similar with its software RAID10 driver in 3-device mode, Windows to me knowledge can not, support on hardware RAID solutions will vary) then that may be the most efficient solution.

Such an arrangement tends to read like RAID0 (must as RAID5 does) but has write performance metrics more like those of RAID1 (unlike RAID5, which can be much much slower for some I/O patterns), gives you the same redundancy of RAID5 (any one device can be in a failed state at any time and the array will recover once the bad device is replaced) and the same usable storage size (twice the size of the smallest drive).

If you are particularly worried about redundancy and potential downtime, then a three-drive RAID1 may be better. This costs space (only getting one drive's worth) but improves resiliency as any two drives can be in a failed state and the array still be fully operational. A good RAID controller will give you a read speed bonus for many load patterns too. If both are supported then I would recommend a three drive RAID1 in place of a two-drive array with a hot-spare because you do not have to wait for the array to rebuild onto the spare when one of the main drives dies and you don't have the risk of the spare failing to spin up when called into action due to not having been used in the X months/years since it was installed. Most if the time single-failed-drive protection is sufficient as double failures are much more rare (except in extreme cases, like a controller failure or power surge that gets as far as the drives, that might well take all the drives out at the same time anyway) and that sort of occurrence is what you network-local online backups are for.