People's speed of hard drives are different. I prefer latency. Other people look at the throughput or bandwidth. Basically latency rules performance while bandwidth follows behind.
RAID-1 (mirroring) will take less load than RAID-5 if assuming we are dealing with software RAID. This means RAID-1 will be a better choice at a latency perspective which means performance. If we care only for throughput, RAID-5 will be better. The write throughput of RAID-1 is not any different compared to a single hard drive. Probably RAID-1 could affect the write performance around 0.1%, so it is nothing to complain about when the setup can be on 24-7 and 365 days a year. Could select RAID-10 which provides a middle ground between latency and throughput.
If selecting a hardware RAID controller from 3ware or Areca, the issues are different since all the load is put on the controller. These controllers includes specialized hardware to handle parity in real-time or faster than real-time, so doing parity checking and creating takes almost an instant. Adding a storage controller does hurt the performance of the computer since it puts a load on the bus and consumes some system registers. A hardware port multiplier could be used instead like the following from Addonics.
http://www.addonics.com/products/hos...d4sr5hpmus.asp
Do not ever think any RAID levels are redundant or gives you security because they do not. They just gives you a chance to keep a computer on 24-7 and 365 days a year.
