Now let’s pass over to SequentialWrite pattern:

Here are the graphs:

Just like in case of SequentialRead, only RAID 0 of four drives stands out here.

Since the four-HDD RAID 0 array manages to write 64KB data blocks much faster than the three-HDD RAID 0 array and starts lagging behind only when the processed data blocks grow really big, Intel SRCS14L controller should be offering too little space for the data in its onboard cache. Of course, the controller processor might be unable to handle such big data packs, however, the XOR-processor is hardly loaded at all in case of RAID 0, so that the data write speed is primarily determined by the controller cache speed and the HDDs performance.

Note that RAID 1 and RAID 10 arrays fall behind the single drive when they read data blocks less than 64KB in size. RAID 5 arrays, on the contrary, start falling behind the single HDD only when the data blocks reach 32KB.

If we disable the lazy write algorithms, the HDDs will work noticeably slower. By the way, this difference in performance proves that the cache of Intel SRCS14L controller, which is always on, cannot handle the entire data flow. In other words, we shouldn’t have blamed the innocent processor.

Now let’s check the controller performance in real practical applications.