Let’s turn to sequential writing now. The WriteBack mode comes first:

The speed of the RAID1 array nearly matches that of the single drive, while the speed of the RAID10 is a little lower than of the two-disk RAID0.

The two- and three-disk RAID0 arrays show good scalability according to the quantity of drives in the array. For the RAID5 arrays, when the data block size is small, the writing speed is higher than that of the single drive or of the “mirror” as R5 Fusion shows itself at work (it “sticks” write requests together in the controller cache). But when the requests are big, there’s simply not enough space in the controller cache (which is four times smaller than the cache of a single HDD). However, if we compare the speeds of the four-disk RAID0 and RAID5 on the 3ware 8506-8 Escalade controller and on the 3ware 8500-8 Escalade controller, we’ll notice that the maximum read speed of the RAID0 grew from 164.9MB/s to 195.7MB/s and the maximum read speed of the RAID5 array grew from 64.3MB/s to 71.4MB/s. This speed growth, especially for the RAID5 array, whose read speed greatly depends on the speed of the XOR processor, makes me think that the Escalade 8506 differs from the Escalade 8500 not only in the support of a faster bus, but also in a higher clock rate of the main chip of the controller (StorSwitch).

Now let’s see how the caching mode affects the performance of four-disk arrays:

By disabling lazy write we greatly reduce the performance of every array!