RAID Levels for SAP BW

Question

I need to know if different raid levels are recommended for SAP BW than for other SAP applications such as R/3.  We are having load performance issues and RAID is one area we are looking at as a potential improvement area.

Answer 1

Hi Jeff,
due to the fact, that SAP has included BI (BW) into NetWeaver, there could no different recommendations for BI and ERP (R/3). I would recommend, that you first should try to find out if you really have an I/O problem.
If you want to find out if you have I/O problems, use TA ST04->"detail analysis" to get the I/O times of the database. On an Oracle system you can get the I/O times on volume level down to the data file level. You'll find the I/O times in milli seconds. You should check if your I/O times are more or less the same on all of your volumes. If not may be you should move some files to disks with lower I/O times.
Normally I/O times should below 10 ms. I/O performance is not good or bad, only you can decide if the performance is good enough or not. As a rule of thumb I would say, that the performance is the better, the more disks you are using. But on current I/O subsystems you have plenty of parameters to vary. Number of disks, stripe size, striping on OS or subsystem level, RAID level, cache size and file system parameters (logging, buffering ...).
As a hint, we run systems on different I/O subsystems and we have I/O times between 12 ms down to 0.8 ms. Needless to say, that the costs of the different systems varies a lot. The 0.8 ms could not be achieved by using only disks, you can only achieve it be using huge caches independent of the RAID level. RAID 10 (1+0) is probably better if you have a lot of random I/O, from a price performance perspective RAID 5 could be better because you have more active disks (more disk space) for the same amount of money.
The bottom line is, you have to decide yourself if your I/O is good enough.