Now, let’s explore the controller’s behavior during sequential writing:
We again organize the arrays into two groups:
RAID0 arrays behave much similar to what they did at sequential reading. Only the 256KB blocks are different as the two-disk RAID0 works faster than all other arrays with them. The graph of RAID1 goes just like the graph of the single drive. Sequential write requests form the most uncomfortable operational mode for RAID5 arrays from the performance point of view, so no wonder that the three-disk array loses to the single drive on 64KB blocks. Well, RAID10 also works slower than the two-disk RAID0.
Let’s disable lazy write for the drives in the arrays and compare the results with those we have got with enabled lazy writing.
100% write requests is the ideal case to illustrate the influence of lazy write of the HDDs on the array speed. When caching is disabled, all arrays suffer a performance hit, although it is quite negligible for RAID0s and RAID10 on <16KB blocks.