Energy Consumption

For our performance testing we used a 3.3GHz (120W TDP) Core 2 X5470; we admit to being a bit paranoid and we wanted the CPU to have plenty of processing power in reserve. In the case of purely storage related tasks, the CPU never achieved more than 15% CPU load with software RAID. Only SysBench was capable of pushing it up to 80%, but if we want to measure the power consumption of our SC-836TQ storage enclosure the SysBench value is unrealistic. In most cases, the server will run the database and perform the transactions. The storage enclosure attached to the server will perform only the I/O processing. Therefore we measure the power consumption of our storage enclosure using IOMeter, and we use a more sensible (80W) 2.5GHz Core 2 E5420 CPU. High performance enclosures (such as those of EMC) also use Xeons to perform the I/O processing.

The SC-836TQ uses one Ablecom PWS-902-1R 900W 75A power supply, one Xeon E5420 "Harpertown", 4x2GB 667MHz FB-DIMM, and one Adaptec 5085 RAID controller. "Full Load" means that the storage enclosure is performing the IOMeter Random Read/Write tests. The difference between sequential reads and random writes is only a few watts (with both SSD and SAS).

Drive Power Consumption
  Idle Full Load Idle
(Drives Only)
Full Load
(Drives Only)
(per Drive)
Full Load
(per Drive)
8 x SSD X25-E 257 275 6 24 0.75 3
4 x SSD X25-E 254 269 3 18 0.75 4.5
8 x SAS (Seagate) 383 404 132 153 16.5 19.125
4 x SAS (Seagate) 316 328 65 77 16.25 19.25
No disks at all
(One system disk)
251 n/a n/a n/a n/a n/a

While the Intel SLC X25-E consumes almost nothing in idle (0.06W), the reality is that the drive is attached to a RAID controller. That RAID controller consumes a little bit of energy to keep the connection to the idle drive alive. Still, the fact that eight SLC drives need 129W less power than eight SAS drives while offering 3 to 13 times better OLTP performance is a small revolution in storage land.

Let us do a small thought experiment. Assume that you have a 100GB database that is performance limited. Our SysBench benchmark showed that eight SLC X25-E drives perform at least three times (up to 13 times) better than ten 15000RPM SAS drives. You need at least 30 SAS drives to achieve the same performance as the SSDs. We'll ignore the fact that you would probably need another enclosure for the 30 drives and simply look at the costs associated with an eight SLC SSD setup versus a 30 drive 15000RPM SAS setup.

We base our KWh price on the US Department of Energy numbers which states that on average 1 KWh costs a little more than 10 cents[2]; the real price is probably a bit higher, but that's close enough. It is important to note that we add 50% more power to account for the costs of air conditioning for removing the heat that the disks generate. We assume that the drives are working eight hours under full load and 16 under light load.

TCO Comparison
  X25-E SAS 15000RPM Comment
Power per drive 1.5 17.375 16 hours idle, 8 hours full load
years 3 3  
KWh per drive (3 years) 38.88 450.36 360 days, 24 hours
Number of drives 8 30 Based on SysBench performance measurements
Total KWh for disks 311.04 13510.8  
Cooling (50%) 155.52 6755.4 to remove heat from array
Total KWh in datacenter 466.56 20266.2 disks power + cooling
Price per KW $0.10 $0.10  
Total Power costs (3 years) $46.656 $2026.62  
TCA $6400 $6000 Eight 64GB SLC drives at $800
Thirty 15000RPM SAS drives at $200
Savings $1579.964    

If you use six drives for the RAID 10 data LUN (two drives for the logs), you need the 64GB SLC drives. That is why we use those in this calculation. Note that our calculation is somewhat biased in favor of the SAS drives: the SLC drives probably run at idle much more than the SAS drives, and it is very likely that even 30 SAS drives won't be able to keep with our eight SSDs. Even with the bias, the conclusion is crystal clear: if you are not space limited but you are performance limited, SSDs are definitely a better deal and will save you quite a bit of money as they lower the TCO.

Testing in the Real World Conclusion
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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.
  • newriter27 - Tuesday, May 5, 2009 - link

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

    Also, how come no response times?

  • 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:">
  • Lifted - Sunday, April 12, 2009 - link

    I like it!
  • 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:">
    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
  • mutantmagnet - Monday, April 6, 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.
  • 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.
  • 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?
  • 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!
  • MrSAballmer - Thursday, March 26, 2009 - link

    SDS with ATA!">">

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