Upgrade Advice: Does Your Fast SSD Really Need SATA 6Gb/s?

Benchmark Results: 4 KB Random Performance

As we noted in our 60/64 GB SSD round-up, we're changing the way we test using Iometer. In the past, we tested random transfers by benchmarking with four workers active in Iometer. This mimics threaded environment, as each worker represents a different application accessing the drive. However, that approach is also overoptimistic because four workers with one outstanding I/O operation each actually translates into a queue depth of four. In order to make things more realistic, we cut the number of workers to one, actually yielding a queue depth of one.

We made two additional tweaks to testing, better tuning the suite for our purposes here today. You see, the average desktop workload experiences a lot of bursty data transfers. However, our prior methodology emphasized sustained performance. In trying to reflect increasingly real-world results, our Iometer scripts now run for one and a half minutes. That's a substantial reduction from our previous scripts that ran for five minutes. Additionally, we're testing queue depths from 0 to 31 in increments of three, since SATA's Native Command Queuing extension only supports that many outstanding commands.

Random Read Performance

Examples include antivirus scans and typing in Word

At a queue depth of one, each SSD performs similarly on a 3 Gb/s or 6 Gb/s connection, except for the SandForce-based Vertex 3.

As you hit seven and sail past 10 outstanding commands, the 3 Gb/s standard constrains the entire field to the 200 MB/s.

Interestingly, Crucial's m4 is substantially slower than the competing 6 Gb/s-capable drives, though it does enjoy a performance boost attached to the faster interface.

For the other two drives (Samsung's 830 and OCZ's Vertex 3), SATA 6 Gb/s demonstrates its benefits at queue depths of four and higher. Once you hit seven outstanding commands, the interface allows these drives to deliver more throughput than a second-gen port would otherwise enable.

Random Write Performance

Examples include email, file compression, and Web browsing

As you can see in the chart below, Samsung's 830, Crucial's m4, and OCZ's Vertex 3 all lose a little bit of performance attached to a 3 Gb/s interface, even at a queue depth of one, accounting for a roughly 9% drop. That's despite the fact that all of these benchmark results fall well under what even a first-gen SATA interface can accommodate.

Although Intel's SSD 320 doesn't impress in this test, the gap between it and other SSDs becomes much wider once you move to a higher queue depth. For example, at more than 10 outstanding I/Os, the 240 GB Vertex 3 and 256 GB m4 top out around 180 MB/s plugged in to a 3 Gb/s port. That's roughly 70 MB/s faster than Intel's SSD 320, which hits its limit at 110 MB/s.

Once you switch to SATA 6Gb/s, the 240 GB Vertex 3 and 256 GB m4 accelerate significantly. At queue depths higher than four, both drives push past the 200 MB/s barrier easily.

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  • If you have a system that is hobbled by a lack of 6Gbs ports yet you have a good PCI spec, you can achieve 6Gbs speeds with a PCI-E card solution such as a RevoDrive. I did just that (even though my machine has 6Gbs SATA ports) as the PCI-E solution is just so simple and practical to use, and depending on which model you choose, it's speed could well exceed even what the reviewed SSDs drives can achieve.
  • The bottleneck these days is the CPU, not the port. My older processor simply can't cope with the amount of data thrown at it by my Vertex 3 240 GB - watch the CPU during an application install for example, I see the CPU maxed out.
  • All this talk of 6gBit upgrades is really annoying.
    I have a PC Express adapter in my Dell laptop that can only achieve averages of 20-30Mbytes to
    a western digital USB3 drive and a PCIe adaptor in my desktop system that randomly acheives 100MB
    for 3-4 seconds before slowng to a 35-40MB crawl for the rest of the transfer to another USB3 drive (reads or writes)

    These are claimed USB2 speeds not USB3.
    The whole thing seems to be a marketing scam for most people. My systems are quite new.
    6Gbit ? dont make me laugh.
    You need to seek out (if you can get it) very expensive upgrades to even get 30% of that speed
    in the real world.