Articles: Storage

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Disk Response Time

For 10 minutes IOMeter is sending a stream of requests to read and write 512-byte data blocks with a request queue of 1. The total of requests processed by each SSD is much larger than its cache, so we get a sustained response time that doesn’t depend on the SSD’s buffer size.

There is nothing to talk about at reading. Every SSD is very good and the difference between them is negligibly small. Yes, the best model is twice as fast as the worst, yet the numbers are all so low that such things like a luckier distribution of load among flash memory banks may be a factor. The RevoDrive may have got its first place thanks to its low-latency interface, but the pursuers are very, very close to it.

Dual-controller solutions feel best at writing as they can alternate write requests between what is actually two SSDs if the requests are arriving in a proper order. The Intel X25-V joins the leaders without having such an advantage, though.

The Crucial C300 is obviously slower than the others when writing 512-byte random-address data blocks irrespective of the interface we connect it with.

Random Read & Write Patterns

Now we will see how the performance of the drives in random read and write modes depends on the size of the requested data block.

Most of the SSDs behave in the same way at random reading. We can only name four products with somewhat lower speeds: the G.Skill, the Vertex 2 with firmware 1.1, the Agility 2 and the pair of Corsair Force drives. The Intel X25-V and the Colossus with two Indilinx chips are ahead when reading very small data blocks but slow down when reading medium-sized ones.

The new testing method offers detailed results for small data blocks, so we can see a tremendous performance leap as the SSDs switch to 4KB chunks of data (the Intel X25-V does not count in because, for technical reasons, its results are approximated from those we achieved with our older method). Why does it happen? Because it is in 4KB blocks that data are written into flash memory chips. Interestingly, we can see this peak not with every SSD but only with the Corsair (both the single SSD and the duo), the OCZ RevoDrive, and the Crucial C300 (with both interfaces).

Another interesting fact is that the chipset-based Corsair array is excellent at writing small data blocks whereas the Crucial C300 is poor then. The latter shows its best when writing random-address data blocks of medium and large sizes and is followed by the RevoDrive.

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