SSD versus Enterprise SAS and SATA disks
by Johan De Gelas on March 20, 2009 2:00 AM EST- Posted in
- IT Computing
Introduction
The introduction of "enterprise SATA" disks a few years ago was an excellent solution for all the companies craving storage space. With capacities up to 1TB per drive, "RAID Enabled" SATA disks offer huge amounts of magnetic disk space with decent reliability. Magnetic disks have been a very cheap solution if you want storage space, with prices at 20 cents per gigabyte (and falling). Performance is terrible, however, with seek times and latency adding a few milliseconds over faster and more expensive alternatives (i.e. SCSI). That's 10,000 to 100,000 times slower than the speed of CPUs and RAM, where access times are expressed in nanoseconds. Even worse is the fact that seek times and latency have been improving at an incredibly slow pace. According to several studies[1], the time (seek time + latency) to get one block of random information has only improved by a factor 2.5 over the last decade while bandwidth has been improved a tenfold. Meanwhile, CPUs have become over 60 times faster! (As a quick point of reference, ten years ago state-of-the-art servers were running 450MHz Xeon processors with up to 2MB of L2 cache.)
The result of this lopsided performance improvements is a serious performance bottleneck, especially for OLTP databases and mail servers that are accessed randomly. A complex combination of application caches, RAID controller caches, hard disk caches, and RAID setups can partially hide the terrible performance shortcomings of the current hard disks, but note the word "partially". Caches will not always contain the right data and it has taken a lot of research and software engineering to develop database management systems that produce many independent parallel I/O threads. Without a good I/O thread system you would not even be able to use RAID setups to increase disk performance.
Let's face it: buying, installing, and powering lots of fast spinning disks just to meet the Monday morning spike on mail servers and transactional applications is frequently a waste of disk space, power, and thus money. In addition, it's not just hard disk space and power that make this a rather expensive and inefficient way to solve the ancient disk seek time problem: you need a UPS (Uninterruptible Power Source) to protect all those disks from power failures, plus expensive software and man-hours to manage all those disks. The Intel X25-E, an SLC SSD drive, holds the potential to run OLTP applications at decent speeds much simpler. Through a deep analysis of its low level and real world performance, we try to find out when this new generation of SSDs will make sense. Prepare for an interesting if complex story….
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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: http://www.intel.com/support/ssdc/index_update.htm">http://www.intel.com/support/ssdc/index_update.htm
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: 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
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!http://www.youtube.com/watch?v=x4dxTRkODbE">http://www.youtube.com/watch?v=x4dxTRkODbE
http://fakesteveballmer.blogspot.com">http://fakesteveballmer.blogspot.com