EXPERT RESPONSE
There are a number of factors to consider when choosing the appropriate RAID level for a specific application. Obviously, cost is one of them, but from the onset, the level of data protection and performance are the two main decisive points. The application's read/write ratio will dictate which RAID level is best suited.
RAID 5 is better suited for mostly read-oriented applications. Because RAID 5 has to write parity information for each block of data it writes to the RAID set, it is not well suited for applications that are "write intensive" such as some transactional databases. It should also be noted that RAID 5 alone does not provide multiple-drive failure protection.
RAID 0+1 offers the same level of data protection as RAID 5 with the addition of multiple-drive failure protection. RAID 0+1 is also better suited for write intensive applications, as its mirroring component (RAID 1) does not need to calculate parity information when writing. In addition, its stripping component (RAID 0) offers the same read performance as RAID 5.
Now, looking at your applications: The MS Exchange Information Store is mostly read-oriented, so it is typically better off on a RAID 5. This is the most cost-efficient way to provide data protection while maintaining read performance. However, MS Exchange also uses logs that can get quite busy. These logs being mostly write-oriented, they will perform better on a RAID 0+1 array. You would have to evaluate the read/write ratio for your database application in order to determine the best type of RAID.
Of course, if your applications are not very busy, the performance distinction between RAID 0+1 and RAID 5 becomes much less noticeable and cost can become the driving factor. Ideally, you should consider a combination of both raid technologies if your disk array allows it.
|
