Performance in Intel IOMeter: File Server & Web Server Patterns

Let’s now see the controller work in modes typical for the disk subsystems of a file- and web-server. The file-server load comes first:

The following diagrams represent the same numbers visually:

There are only 20% of write requests in this pattern, so all the arrays have very good speeds. The RAID0 performance scales up depending on the number of drives in the array. The speeds of the RAID1 and the RAID10 are near those of the 2-disk and 4-disk RAID0, respectively, and it means the algorithm for optimal reading from a mirror works perfectly here. So the 4-disk RAID5 is the only to act up – at the queue depth of 256. There’s something wrong with this array at high loads in all the patterns.

We are going to compare the arrays by calculating their performance ratings. Since each load has the same probability, the performance rating is the averaged speed of the array under all loads:

The 4-disk RAID0 is quite far ahead of the others. The RAID10 takes the second place and the 3- and 4-disk RAID5 arrays are a little slower than the 2- and 3-disk RAID0 arrays, respectively. The RAID1 is on the last but one position, but is still much faster than the single drive.

Let’s see if these results change in WriteThrough caching mode.

Even 20% of write requests is enough for all the arrays to perform differently in WriteBack mode than in WriteThrough. The RAID5 acts up again at the queue of 256 requests.

This is how the caching mode affects the performance rating of an array:

So it is clear that turning WriteBack caching off in modes with some write requests results in a performance reduction.