28th October 2009

SATA vs. SAS vs. SSD

posted in Technology |

I was doing some analysis recently and I put together a simple comparison chart between commodity SATA drives, enterprise SAS drives and enterprise SSD. Often SSD is positioned as “fast but very expensive”. But expensive is all a matter of what you are measuring. SSD is VERY expensive for capacity, but realtively inexpensive for performance.

  Commodity SATA
$100 1TB 75IOPS		 Enterprise SAS
$200 146GB 125IOPS		 SSD
Intel X25E 64GB
$700 64GB 3300IOPS
GB/$ 1 (10GB/$) .07(.7GB/$) .009 (.09/$)
IOPS/$ 1 (.75/$) .83 (.625/$) 6.29 (4.71/$)

First numbers in each cell are normalized to the SATA drives.

The table above makes it pretty clear just how different these technologies are. The SSD is 100x more expensive per GB than the commodity SATA drive. But when you measure based on IOPS it is 6x cheaper. You would need 44 spindles of traditional drives to match the I/O performance of a single SSD. Before I go on, I should point out the measurements aren’t apples to apples. The SSD measurement is write performance. The SATA performance varies a ton depending on the type of operations. Sequential reads and writes can be quite efficient while a SSD doesn’t benefit from larger reads & writes beyond a certain point.

It is also interesting to observe that the SAS drives appear to never make sense. They are 50% faster than the SATA drives but they cost so much more that it is hard to imagine a scenario where they would be the right choice.

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There are currently 4 responses to “SATA vs. SAS vs. SSD”

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  1. 1 On October 30th, 2009, Dave Naffziger said:

    Great summary - one of the better ones I’ve seen yet. While GB/$ should go up, I’d also expect IOPS/$ to rise as well. We’re finding IOPS to be the limiting factor in most of the cloud stuff we’re doing.

  2. 2 On October 30th, 2009, Alex said:

    Often true- this stuff gets complicated when you need to apply real world usage patterns to the analysis. But future trends are also interesting to think about. Commodity SATA will likely continue to gain against SSD in GB/$, but I’d expect SSDs to get even faster (and 6Gb SATA will help them more too) while SATA drives will likely have constant performance characteristics.

  3. 3 On March 25th, 2010, KCockrell said:

    “…interesting to observe that the SAS drives appear to never make sense…”

    Reliability of commodity SATA is their biggest issue, and the most compelling SAS argument.

  4. 4 On April 6th, 2010, Alex said:

    KCockrell- good point, but two things. First of all, despite the manufacturer specs, I’ve read several sources where they didn’t find real world (data center) reliability to be actually meaningfully different. Second, in any larger system you are going to have tons of failures of devices either way. With the SATA drives its easy to over-provision a bunch more (without adding too much cost)so even with a ton of failures everything keeps running smoothly.

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