Adventures in RAID

Recently, we had an issue with an IIS web server that was displaying unusually poor performance. It was running a business application that had 100+ users hitting the web server with a continuous stream of requests to download 50 KB image files (dozens per second). The server was configured with a software RAID 0 controller for the drive with both the web site and the OS. This created an I/O bottleneck condition on the server. After converting this to RAID 1+0 using a hardware controller, the performance increased dramatically.

System tests using a single drive, non-RAID configuration had performed better than this server with a RAID 0 software controller.

RAID is primarily a cost effective configuration for disk storage to increase performance with improvements in reliability for certain RAID levels. However, using software controllers and levels that offer only marginal benefits like RAID 0 may do more harm than good. The moral of this story is to consider carefully the value of RAID configurations and do not assume that because it says “RAID” that it is better.