Use RAID to increase write performance on three-drive arrays

On many small servers with RAID 5, you'll see the minimum three-drive array. Although read access on a three-drive array is faster than on a single drive, write performance is abysmal. If price is a consideration, a simple RAID 1 (i.e., hardware-mirrored) pair will show much better write performance.

I see many small servers with RAID 5, and sadly, a three-drive array (the minimum) is often chosen.

Although read access on a three-drive array is faster than on a single drive (read access is calculated as n times the number of drives for RAID 0, 1, 5, 6 and 1,0), write performance is abysmal -- 75% that of a single drive! This lack of performance becomes evident as system slowdowns occur during heavy write operations, especially single-threaded ones.

If price is a consideration, a simple RAID 1 (i.e., hardware-mirrored) pair will perform more consistently. In fact, write operations will be 33% greater than a three-drive RAID 5 setup.

Another option is to add one more drive and chose RAID 1,0. If you choose this route, read performance will be 33% greater than three-drive RAID 5, and write performance will be 2.7 times greater.

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This was first published in June 2007
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