Disk strategies

With magnetic disks, there are two strategies to get good OLTP or mail server performance. The "traditional way" is to combine a number of 15000RPM SAS "spindles", all working in parallel. The more "rebellious way" or "Google way" is to use a vast number of cheaper SATA drives. This last strategy is based on the observation that although SATA drives come with higher access times, you can buy more SATA spindles than SAS spindles for the same price. While Google opted for desktop drives, we worked with what we had in the lab: 16 enterprise 1TB Western Digital drives. Since these are one of the fastest 7200RPM drives that can be found on the market, it should give you a good idea what an array with lots of SATA drives can do compared to one with fewer fast spinning SAS drives.

SSDs add a new strategy: if space is not your primary problem, you can trade in storage space for huge amounts of random I/O operations per second, requiring fewer but far more expensive drives to obtain the same performance. SSDs offer superb read access times but slightly less impressive write access times.

As Anand has pointed out, a cheap SSD controller can really wreak havoc on writing performance, especially in a server environment where many requests are issued in parallel. EMC solved this with their high-end Enterprise Flash Disks, produced by STEC, which can store up to 400GB and come with a controller with excellent SRAM caches and a super capacitor. The super capacitor enables the controller to empty the relatively large DRAM caches and write the date to the flash storage in the event of a sudden power failure.

Intel went for the midrange market, and gave its controller less cache (16MB). The controller is still intelligent and powerful enough to crush the competition with the cheap JMicron JMF602-controllers. We check out the SLC version, the Intel X25-E SLC 32GB.

The newest Intel Solid State Disks with their access times of 0.075 ms and 0.15W power consumption could change the storage market for OLTP databases. However, the SLC drives have a few disadvantages compared to the best SAS drives out there:

  • No dual ports
  • The price per GB is 13 times higher

You can see the summary in the table below.

Enterprise Drive Pricing
Drive Interface Capacity Pricing Price per GB
Intel X25-E SLC SATA 32GB $415-$470 $13
Intel X25-E SLC SATA 64GB $795-$900 $12
Seagate Cheetah 15000RPM SAS 300GB $270-$300 $0.90
Western Digital 1000FYPS SATA 1000GB $190-$200 $0.19

If you really need capacity, SATA or even SAS drives are probably the best choice. On the other hand, if you need spindles to get more I/O per second, it will be interesting to see how a number of SAS or SATA drives compares to the SLC drives. The most striking advantages of the Intel X25-E SLC drive are extremely low random access times, almost no power consumption at idle, low power consumption at full load, and high reliability.

Enterprise Drive Specifications
Drive Read Access Time Write Access Time Idle Power Full Power MTBF
(hours)
Intel X25-E SLC 32GB 0.075 ms 0.085 ms 0.06 W 2.4 W 2 million
Intel X25-E SLC 64GB 0.075 ms 0.085 ms 0.06 W 2.6 W 2 million
Seagate Cheetah 15000RPM 5.5 ms (*) 6 ms 14.3 W 17 W 1.4 million
Western Digital 1000FYPS 13 ms (**) n/a 4 W 7.4 W 1.2 million

(*) 5.5 ms = 3.5 ms seek time + 2 ms latency (rotation)
(**) 13 ms = 8.9 ms seek time + 4.1 ms latency (rotation)

Reliability testing is outside the scope of this document, but if only half of the Intel claims are true, the x25-E SLC drives will outlive the vast majority of magnetic disks. First is the 2 million MTBF specification, which is far better than the best SAS disks on the market (1.6 million hour MTBF). Intel also guarantees that if the X25-E performs 7000 8KB random access per second, consisting of 66% reads and 33% writes, the drive will continue to do so for 5 years! That is 2.9TB of written data per day, and it can sustain this for about 1800 days. That is simply breathtaking as no drive has to sustain that kind of IOPS 24 hours per day for such a long period.

Index Configuration and Benchmarking Setup
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  • shady28 - Sunday, November 15, 2009 - link


    I would have really like to see single drive performance of SAS 15K drives vs SSDs. The cost of a SAS controller ($60) + a 15K 150Gig drive ($110-$160) is less than any of the high end SSDs, and about the same as a low end SSD. It's a viable option to get a 15K Drive, but very difficult to see what is the best choice when looking at RAID configs and database IOPs.
    Reply
  • newriter27 - Tuesday, May 05, 2009 - link

    What was the Queue Depth setting used with IOmeter? Was it maintained consistently?

    Also, how come no response times?

    Reply
  • mikeblas - Friday, April 17, 2009 - link

    Intel has posted a firmware upgrade for their SSD drives which tries to address the write leveling problem. The patch improves matters, somewhat, but the overall performance level from the drives is still completely unacceptable for production applications.

    You can find it here: http://www.intel.com/support/ssdc/index_update.htm">http://www.intel.com/support/ssdc/index_update.htm
    Reply
  • Lifted - Sunday, April 12, 2009 - link

    I like it! Reply
  • turrican2097 - Monday, March 30, 2009 - link

    Please mention or correct this on your article.
    1) You should mention that the price per GB is 65x higher than the 1TB drives, since you chose to include them.
    2) Your WD is a poor performance 5400RPM Green Power drive: http://www.techreport.com/articles.x/16393/8">http://www.techreport.com/articles.x/16393/8
    3) If you make such a strong point on how much faster SSDs are than platters, you can't pick the best SSD and then use the hardrives you happen to have laying around the lab. Pick Velociraptors or WD RE3 7200RPM and then Seagate 15K7.

    Thank you
    Reply
  • mutantmagnet - Monday, April 06, 2009 - link

    It's irrelevant. Raptors don't outperform SAS which are better in terms of performance for the GB paid for. There's no need to belittle them when they are clearly aware of the type of point you are making and went beyond it.

    So far I've found these recent SSD articles to be a fun and worthwhile read; and the comments have been invaluable, even if some people sound a little too aggressive in making their points.
    Reply
  • virtualgeek - Friday, March 27, 2009 - link

    Just wanted to point this out - we are now shipping these 200GB and 400GB SLC-based STEC drives in EMC Symmetrix, CLARiiON and Celerra. These are the 2nd full generation of EFDs.

    Gang - this IS the future of performance-oriented storage (not implying it will be EMC-unique - it won't be - everyone will do it - from the high end to the low end) - only a matter of time (we're currently at the point where they are 1/3 the acquisition cost to hit a given IOPS workload - and they have dropped by a factor of 4x in ONE YEAR).

    With Intel and Samsung entering to the market full force - the price/performance/capacity curve will continue to accelerate.
    Reply
  • ms0815 - Friday, March 27, 2009 - link

    Since modern Graphic cards crack passwords more than 10 times faster than a CPU, wouldn't they also be greate Raid Controllers with their massive paralel design? Reply
  • Casper42 - Thursday, March 26, 2009 - link

    I would have liked to have seen 2 additional drives tossed into the mix on this one.

    1) The Intel X25-M - Because I think it would serve as a good middleground between the SAS Drives and the E model. Cheaper/GB but still gets you a much faster Random Read result and I'm sure a slightly faster Random Write as well.

    2) 2.5" SAS Drives - Because mainstream servers like HP and Dell seem to be going more and more this direction. I don't know many Fortune 500s using Supermicro. 2.5" SAS goes up to 72GB for 15K and 300GB for 10K currently. Though I am hearing that 144GB 15K models are right around the corner.

    Thanks for an interesting article!
    Reply
  • MrSAballmer - Thursday, March 26, 2009 - link

    SDS with ATA!

    http://www.youtube.com/watch?v=x4dxTRkODbE">http://www.youtube.com/watch?v=x4dxTRkODbE

    http://fakesteveballmer.blogspot.com">http://fakesteveballmer.blogspot.com
    Reply

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