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SSD 2011 roundup: Crucial M4, OCZ Vertex 3, Intel 510/320
by Marc Prieur
Published on June 23, 2011

Random reads
We then moved on to random accesses, looking at reads first of all. Of course in standard usage, reads are far more common than writes and when it comes to a system disk, random accesses are of primary importance, especially in intensive multitasking. A storage device’s capacity to process a large number of random accesses, something that is directly linked to access times, is what will save it from slowing down the rest of the PC when it’s asked to access data situated in several places at the same time.

A standard hard drive with an access time of 10ms won’t manage more than 100 operations per second (IOPS), while SSDs have access times of between 0.13 and 0.23ms, or 7800 to 4300 IOPS. A huge difference! As in the previous test we measured random accesses on an Intel SATA 6G port and, in addition, on an Intel SATA 3G port for the 6G SSDs and with compressible or incompressible data with the SandForces.

The tests were carried out with 1, 2, 4, 8, 16 and even 32 simultaneous accesses (QD1 to 32 in the graphs). This gives us an understanding of an SSD’s capacity to process these accesses in parallel, with the ideal scenario being that performance is doubled between 1 and 2, 2 and 4 and so on. While it’s definitely worth checking this out, we shouldn’t lose sight of the fact that in standard usage, the level of simultaneous accesses is somewhere between 1 and 4.

MB/s: [ 3G/6G - Incomp. ]  [ 3G/6G - Comp.]  [ 3G - Incomp. ]  [ 3G - Comp. ]
IO/s: [ 3G/6G - Incomp. ]  [ 3G/6G - Comp.]  [ 3G - Incomp. ]  [ 3G - Comp. ]


MB/s: [ 3G/6G - Incomp. ]  [ 3G/6G - Comp.]  [ 3G - Incomp. ]  [ 3G - Comp. ]
IO/s: [ 3G/6G - Incomp. ]  [ 3G/6G - Comp.]  [ 3G - Incomp. ]  [ 3G - Comp. ]

While the new generation SSDs give substantial sequential speed gains, the same can’t be said for random speeds. Worse, none of the new SSDs can match the performance levels managed by the C300!

This is notably the case for the Crucial M4, which is however the fastest of the new SSDs tested. The 128 GB version actually obtains markedly better results than the 256 GB version. The explanation for this is in fact fairly simple and is down to the memory chips used. On the 128 GB version, the chips used are organised with pages – the smallest readable unit – of 4 KB, whereas the 256 GB version is constituted of 8 KB pages. To read the 4 KB blocks required in this test, the 256 GB version therefore has to access a full 8 KB page.

The Intel SSD 320s are in second position with not much difference in performance between the two capacities. They’re more or less comparable to the X25-M from QD1 to QD8 and do better beyond that.

The Intel SSD 510s and Vertex 3s are the slowest of the new generation SSDs here. The Intel SSD 510s are faster from QD1 to QD4, the most common loads in standard usage, while the Vertex 3s are in front beyond this.

The SandForce SSDs do vary depending on the type of data, but not by much. The impact of the 3G limitation on 6G SSDs is generally low, but noteworthy, especially with the C300 256, C300 128 and M4 128, which are then limited to 190 MB/s at QD32 while they manage 220 – 236 MB/s at SATA 6G.

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