Next we will check the controller’s speed at sequential writing. The speeds of the arrays at different data block sizes are shown below, in WriteBack mode:

We again split the arrays in two groups and create diagrams to show the dependence of the array speed on the data block size.

Just like at sequential reading, the advantages of the RAID0 arrays with more hard drives show up only at large data block sizes. And while the 2-disk RAID0 reached its maximum speed on 64KB blocks, the 3-disk array did the same on 256KB blocks only, and the 4-disk array did not reach the maximum speed even on 1024KB data blocks, possibly limited by the performance of the I/O processor.

The speeds of the mirroring RAID1 and RAID10 arrays almost coincide with the speeds of the single drive and the 2-disk RAID0, respectively, now that there are no read requests to be served. The RAID5 arrays speed up towards 64KB data blocks and then from 128KB blocks onwards.

You can compare these numbers to the WriteThrough mode results :

Here’s a comparative diagram for 4-disk arrays:

100% write requests is the ideal case to show how write-caching influences the performance of an array. Every array is much slower when caching is off!