Articles: Storage

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Disk Response Time

In this test IOMeter is sending a stream of requests to read and write 512-byte data blocks with a request queue depth of 1 for 10 minutes. The total amount of requests processed by the drive is much more than its cache buffer, so we get a sustained response time that doesn’t depend on the amount of cache memory the drive has.

We can see obvious improvements here. The new interface has lower latencies than its predecessor but cannot match SATA 300. You can see this from the results of the Vantec enclosure in which we used the same HDD as connected via SATA. The Buffalo enclosure contained another sample of the same HDD model and performed differently. It may have a slow chip with poorly optimized firmware, yet we are prone to explain this by the difference between the HDDs. For example, the results of the SSD installed into the Vantec show that the interface does not increase the response time much above the SSD’s own response time. Thus, the interface’s influence is rather low in this test.

Random Read & Write Patterns

Now we will check out the dependence between the drives’ performance in random read and write modes on the size of the processed data block.

We will discuss the results in two ways. For small-size data chunks we will draw graphs showing the dependence of the amount of operations per second on the data chunk size. For large chunks we will compare the drives’ performance basing on the data-transfer rate in megabytes per second.

The new interface does not differ much from the older one when it comes to processing small data blocks. Both are somewhat inferior to SATA 300, yet it is the HDD rather than the interface that determines the resulting speed then. But when it comes to large requests (1 or 2 megabytes, which is similar to viewing photos from a fragmented disk), the new interface performs much better than the old one. Vantec’s USB 3.0 implementation is definitely better as it is but slightly slower than the HDD connected via SATA. The gap between the two USB 3.0 enclosures grows larger when the size of the processed data blocks increases.

We’ve got a different picture at writing. The SATA drive is faster with small data blocks whereas the peripheral interfaces deliver similar performance, being about half as fast as the leader. With large data blocks the USB 3.0 interface gets closer to the leader. USB 2.0 reaches its maximum speed at 2MB data blocks whereas SATA and USB 3.0 keep on accelerating. The Vantec is again considerably better than the Buffalo although the latter behaves more predictably.

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