SSD versus Enterprise SAS and SATA disks
by Johan De Gelas on March 20, 2009 2:00 AM EST- Posted in
- IT Computing
IOMeter/SQLIO Software Setup
Before we start with the "closer to the real world" OLTP tests, we decided to measure the disk component part of database performance with IOMeter and SQLIO. For these tests, we started with RAID 0 as we didn't want our RAID controller to be the bottleneck. Some benchmark scenarios showed that our hopes were in vain, as sometimes the RAID controller can still be the bottleneck as you will see shortly. We selected a 64KB stripe size as we assumed the intended use was for a database application that has to perform both sequential and random reads/writes.
As we test with SQLIO, Microsoft's I/O stress tool for MS SQL server 2005, it is important to know that if the SQL server database accesses the disks in random fashion this happens in blocks of 8KB. Sequential accesses (read-ahead) can use I/O sizes from 16KB up to 1024KB, so we used a stripe size of 64KB as a decent compromise. All tests are done with Disk Queue Length (DQL) at 2 per drive (16 for an eight drive array). DQL indicates the number of outstanding disk requests as well as requests currently being serviced for a particular disk. A DQL that averages 2 per drive or more means that the disk system is the bottleneck.
Next we aligned (more info here) our testing partition with a 64KB offset with the diskpart tool. There has been some discussion on the ideal alignment (512KB, one block?), but even Intel is not sure yet. So we chose the relatively safe 64KB boundary (which aligns with 4KB pages).
To keep the number of benchmarks reasonable, we use the following:
- RAID 0, RAID 10, or RAID 5; stripe size 64KB (always)
- Adaptive Read Ahead and Write-Back always configured on the RAID controller
- NTFS, 64KB cluster size
- Access block size 8KB (Random) and 64KB (Sequential)
This should give you a good idea of how we tested. The controllers available only support eight drives. As we wanted to test the "use more cheaper SATA disks" philosophy, we use two controllers combined with Microsoft's software RAID to test 16 drives. Software RAID is at least as fast as hardware RAID as we use the mighty 2.5GHz quad-core Xeon instead of the small dual-core Intel IOP 348 controller.
To make the graphs easier to read, we made all SATA disks measurements orange, all SAS disks measurements green, and all SATA-SSD benchmarks are blue.
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marraco - Wednesday, March 25, 2009 - link
The comparison is not fair, but can be fairer:If the RAID of SATA/SAS disks is restricted to the same storage capacity than the SSD, limiting the partition to the fastest external tracks/cilynders, the latency is significantly reduced, and average read/write speed is significantly increased, so
PLEASE, PLEASE, PLEASE
Repeat the benchmarcks, but with short stroking for magnetic disks.
JohanAnandtech - Friday, March 27, 2009 - link
May I ask what the difference with the fact that we created a relatively small partition across our RAID-5 raidset? Also, you can imagine that our 23 GB database was at the outer tracks of the disks. I have to verify, but that seems logical.This kind of testing should give the same effects as short stroking. I personally think Short stroking can not be good for your actuator, while a small partition should be no problem.
marraco - Friday, March 27, 2009 - link
See this link.http://www.tomshardware.com/reviews/short-stroking...">http://www.tomshardware.com/reviews/short-stroking...
Clearly, you results are orders of magnitude than those showed on that benchmark.
As I understand, short stroking increase actuator health, because reduces physical acceleration on the actuator.
Anything necessary, is to use a small partition on the fastest external track.
you utilized a raid 0 of 16 disks, with less than 1000 gb/second.
On Tomshardware, a raid of only 4 disk achieved average (not maximun) 1400 to 1600 Mb/s. (of course, the test are not the same; for that reason, I ask for new test)
About the RAID 5: I would love to see RAID 0.
I are interesed on comparing a fast SSD as the intels, (or OCZ Vostro/Summit), with what can be achieved at the same cost, with magnetic media, if the partition size is restricted to the same total capacity than the SSD.
Anyway, thanks for the article. Good work.
So good, I want to see more :)
marraco - Sunday, April 5, 2009 - link
Please, tell me you are preparing such article :)JohanAnandtech - Tuesday, April 7, 2009 - link
We are investigating the issue. I like to have some second opinions before I start heavy benchmarking on THG article. They tend to be sensational...araczynski - Wednesday, March 25, 2009 - link
wow, color me impressed. all the more reason to upgrade everything to gigabit and fiber.BailoutBenny - Tuesday, March 24, 2009 - link
Can we get any updates on the future of chalcogenide glass (phase change) based drive technologies? IBM's Millipede and other MEMS probe storage devices? Any word about Intel and STMicroelectronics' shipments of PRAM samples to customers that happened last year? What do the rumor mills say? Are these technologies proving viable? It is difficult to formulate a coherent picture for these technologies without being an industry insider.Black Jacque - Tuesday, March 24, 2009 - link
RAID 5 in Action... However, it is rarely if ever used for any serious application.
You are obviously not a SAN Admin or know too much about enterprise level storage.
RAID 5 is the mainstay of block-level storage systems by companies like EMC.
In addition, the article mentions STEC EFDs used by EMC. On the EMC CLARiiON line, those EFDs are provisioned in RAID 5 groups.
spikespiegal - Wednesday, March 25, 2009 - link
[quote]RAID 5 is the mainstay of block-level storage systems by companies like EMC. [/quote]Which thus explains why in this day in age I see so many SANs blowing entire volumes and costing days of restoration when the room temp gets a few degrees above ambient.
Corrupted RAID 5 arrays have cost me more lost enterprise data than all the non-RAID client side disks I've ever replaced; iSeries, all brands of x386, etc. EMC has a great script to account for this in which they always blame the drives first, then only when cornered by an enraged CIO will they admit it's their controllers. Been there...done that...for over a decade in many different industries.
If you haven't been burned by RAID 5, or dare claim a drive controller in RAID 5 mode has a better MTBF than the drives it's hosting, then it's time to quite your day job at the call center in India. RAID 5 saves you the cost of one drive every four, which was logical in 1998 but not today. At least span across multiple redundant controllers in RAID 10 or something....
JohanAnandtech - Tuesday, March 24, 2009 - link
I fear you misread that sentence:"RAID 0 is good way to see how adding more disks scales up your writing and reading performance. However, it is rarely if ever used for any serious application."
So we are talking about RAID-0 not RAID-5.
http://it.anandtech.com/IT/showdoc.aspx?i=3532&...">http://it.anandtech.com/IT/showdoc.aspx?i=3532&...