Now let’s view the results of the same test, but in the write-back mode. First, the table:

And the diagrams:

I’m going to single out discrepancies in the graphs compared to the write-through mode. The numbers will follow.

First of all, the graphs have bends now which are imposed by another optimization, the controller’s lazy write.

The second noticeable difference from the write-through mode is that the RAID5 arrays are speeding up when the writes percentage grows. For the first time we see the RAID5 arrays of three and four disks showing different speeds, although in three modes only. Their acceleration is explained by the fact that write requests are now additionally optimized by the controller’s cache. The mirrors, RAID1 and RAID10, are always faster than the JBOD and the two-disk RAID0, respectively, save for the Random Write mode (100% write requests).