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I/O Performance In Abundance

SSDs In RAID: A Performance Scaling Analysis
By , Achim Roos

Sequential read rates of more than 200 MB/s no doubt speak for SSDs, but whether the drive peaks at 230 or even 260 MB/s is of less importance when it comes to professional use. What is more important, especially in servers, is the number of I/O operations such a system can handle per second. Because the access times of SSDs are in the microsecond range, they outclass traditional hard drives in this respect.

HDD versus SSD: where magnetic drives can only handle a few hundred I/Os per second, current SSDs are delivering five-digit values. Source: SamsungHDD versus SSD: where magnetic drives can only handle a few hundred I/Os per second, current SSDs are delivering five-digit values. Source: Samsung

Using the right flash drive can increase the I/O performance at a factor of up to three digits, according to Korean manufacturer Samsung. The image above shows the I/O performance of Samsung’s current generation of SSDs compared to a 15 000 RPM SAS hard drive, demonstrating a whooping 106-fold performance increase. In our own testing, we found this performance advantage to be similar on many flash drives. In our comparison tests of the best SSDs we particularily noticed major differences in I/O performance between the various participants. But, apart from some unsuitable candidates, even the lower- to middle-class SSDs outperform current enterprise hard drives by a factor of at least 10, on average.

Power Saving With SSDs

Another important reason for the use of SSDs in enterprise environments is the lower power consumption of the devices. While good flash drives never exceed their maximum load claims of 2 W, and do not use even 10% of that at idle, enterprise hard drives frequently use 10 W or more. These are all certainly very low numbers, but important nevertheless.

Server hard drive installations in data centers are real power hogs, costing accordingly. The Fraunhofer Institute and market analysis group IDC estimate that air conditioning makes up about 50% of the total power consumption in data centers. Obviously, that's significant. With SSDs however, low power consumption and high I/O performance go hand-in-hand. The I/O per watt ratio is both reliable and often quoted, ensuring that energy efficiency stays relative to performance, which also speaks for the use of flash drives.

Expandability Of SSD RAIDs

For enterprises, it may well be worth the cost to replace a hard drive-equipped server with a flash-based system. Take the significantly higher I/O values, lower energy consumption, and heat generation into consideration and the calculation may still favor SSDs, despite the individual flash drives being more expensive to replace and storage capacities almost always smaller. And of course, you have to take into account how many SSDs would be needed to enhance the performance of an existing multi-hard drive system.

However, the most interesting question, by far, is about the expansion capability of an SSD server. We have a test system up and running to examine the scalability of SSD RAID arrays.

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  • 0 Hide
    campb292 , March 26, 2011 1:44 AM
    Ask GR what he thinks.
  • 1 Hide
    mrbongal007 , March 26, 2011 3:16 AM
    hi, pls help in understanding how are you getting 1000 MB/s performance on a sata3 port/lane which gives max of 600MB/s. if the answer is raid striping across 5 lanes then potentially we can get this performance on a sata2 port as well since each lane is being taxed to appx 200MB/s. appreciate your help in understanding this. thanks.
  • 1 Hide
    oxxfatelostxxo , March 26, 2011 3:32 AM
    OutPut is through a pci x8 slot. Max transfer of 6gb/s I think. The sata 2 max is per channel for each drive. Not a combined max
  • 0 Hide
    chefboyeb , March 26, 2011 5:01 AM
    I guess i would be better off adding 2 more ocz vertex ssds to my existing 3 ssd raid 0 setup afterall... I was concerned about the limitations of motherboard, but not anymore... Thanks
  • 1 Hide
    oxxfatelostxxo , March 26, 2011 5:14 AM
    ... The motherboard will Max out. You need a raid card to see those speeds
  • 0 Hide
    saymi , March 26, 2011 6:24 AM
    Sasmsung!
  • 0 Hide
    Anonymous , March 26, 2011 7:04 AM
    maybe is just me only.
    3 reason hold me back moving HD to SSD.
    1st. money VS pre GB.
    2nd. the technology is mature enough to keep that real speed in stabilize performance.
    3rd. RAID support in SSD still in wonderland.
    conclusion. all the read/write speed in the benchmark is full of BS, but if you can maintain the driver is reading purpose only but never erase and delete any old data and rewrite new files into it. and you are a heavily download user. you will lost the speed advance reading/writing in a SSD over a traditional HD. SSD is pretty fast only in a fresh windows install for the first time. it will lose speed performance in time and you have to do another fresh reinstall again and again.
  • 0 Hide
    Anonymous , March 26, 2011 7:05 AM
    2nd. the technology is not mature enough to keep that real speed in stabilize performance.
  • 0 Hide
    nebun , March 26, 2011 8:37 AM
    oxxfatelostxxo... The motherboard will Max out. You need a raid card to see those speeds

    or just use an PCIE SSD like the revodrive x2 :)  no limit
  • 0 Hide
    parpanghel , March 26, 2011 8:44 AM
    Yeah right, SASMSUNG drives are the best :-} too much souce last night my fren' ?
  • -2 Hide
    oxxfatelostxxo , March 26, 2011 9:08 AM
    To ssdlkje
    1: Money vs gb.. they arn't really that expensive anymore, after rebate i spent 180$ for 2 60gb ssds, and put them in raid 0 for my OS. Runs perfect and not too expensive.

    2: My SSD's constantly get files written to them, i have yet to see any loss in performance. 6 months so far with same windows install.

    3: Raid support in wonderland? not sure what you mean.., you can put them in a raid just like a hdd. Works exactly the same.

    @ Nebun: yea you can use a revodrive, but if you look at reviews very glitchy and lots of issues. Not to mention you would get better performance with a raid card and ssd's for about the same price.
  • 5 Hide
    hixbot , March 26, 2011 9:19 AM
    I would really love to see an article evaluating degraded performance in RAID vs degraded performance in single drive. Trim Vs Garbage Collection etc, and all our options to keep performance at its best in RAID.
    How do different consumer model SSDs handle degraded performance in RAID operation?

    Also it would be nice to see how many RAID 0 SSDs can a typical onboard RAID controller handle before the linear performance model breaks down.
  • 0 Hide
    Anonymous , March 26, 2011 10:07 AM
    interesting posts and article. I wonder if the use of a VHD (Windows 7) file for the OS volume would be the answer to future performance degration. There is a performance hit because it is a VHD, but it should be negligible because of the performance gains from the SSD and RAID 0.
  • 0 Hide
    Anonymous , March 26, 2011 10:51 AM
    re: oxxfatelostxxo
    good for you. but I suggest you do a benchmark for yourself. I m not sure
    is just probably only happens to me. I spent $1000$ to get 4 SSD 6 month ago from newegg. try to set up it as raid 0 in my workstation for a better file cache speed for any purpose such as render or fluid simulation. it drive me crazy just try to set things up right. 4 SSD in raid 0 will lose the function on trim. and garbage collector is never be a another good solution either. so I sold it on ebay. until intel or anyone can come up with a better comparable raid card for SSD with full trim support even in any raid mode. I will give another try. but for now 6 tradition HD in raid 0 average speed 250 read/write. good but not the best and less problem.
  • 0 Hide
    JohnnyLucky , March 26, 2011 1:54 PM
    I read a similar report about a company over on the mainstream side. They created a massive array using Intel enterprise ssd's. It was amazing what they were able to accomplish.
  • 0 Hide
    emperornicon , March 26, 2011 2:48 PM
    If I understand things right, the folks dealing some these types SSD Drives said they tend to degenerate or degrade over their life span. I am one of the lucky individuals that live on a Raid-0 system 365year. I own six of the Western Digital 250 GB WD2500AAKS-00UU3A0 these drives all have a 16 Mb buffer of course running SATA II 3.0 GB/S speeds and cost $47.99 each they boast a 631.3 MB/sec average write 231.6 MB/sec average 1500 GB but really 1396.9 GB volume. Each drive by itself reads at an average rate of 130.2 Mb/s then writes at an average of 76.4 Mb/s. My Raid-0 array should be reading at 781.2 Mb/s, and then it should be writing at 458.4 Mb/s this must be from some kind of overhead.
    My personal computer consist of these parts and configurations; Micron 8 GB ECC 1600 MHz 7-7-7-27-1T 8*200 MHz 1.5V 2 GB * 4 sticks and OC’D @ 1666 MHz 8-8-8-30-1T 8 * 250 MHz 1.65V. My Processor AMD Phenom II X6 1090T 3.2 GHz 1.3V @ 4125 MHz 16.5*250 1.45V on a 64bit OS, and @ 4375 MHz 17.5*250 1.45V on a x86 OS Utilizing a Gigabyte GA-MA790XT-U4DP motherboard F8G BIOS. Then I am using the Corsair H50 water cooler with custom Heat spreaders for my ram. Finally my graphics card is an ATI Radeon HD 5870 1GB DDR5 stock clock.
    On the other hand, should I be content that I am able to install windows XP 2k3 or 2k8 in 5min and Linux Fedora 13, Ubuntu 10.10 and Centos 5 in 3min of course my Installs are unattended not from a DVD disk.

    1. Should I really replace my disks with SSD Drives?
    2. Is the expense worth cost, not thinking of performance of electrical efficiency in mind?
    3. How does the SSD category’s score in reliability in terms of being trusted with mission critical data with patient health care records?
    4. Is it possible for the SSD Drives out live mechanical Hard disks in terms of MBTF?
    5. Is this storage technology still in its infancy?
    6. Will the price SSD Drive ever lower to compete with traditional storage?
  • 0 Hide
    marraco , March 26, 2011 3:47 PM
    I want a faster RAID 0, but I also want to buy new drives, and add them to my old RAID.

    Problem is that new drives have different speeds (and also are larger). So, I need “Asymmetric RAID 0”. A technology which not exists, but would be easy to implement. An Asymmetric RAID 0 controller should distribute data in proportion to the speed of each drive. Small Chunks of data to slow drives, and largest bits of data to faster drives. Otherwise, the slower drives would bottleneck the faster ones. (It means different sizes of partitions, each one proportional to the drive speed).

    I also want to know scaling on integrated RAID controllers like the ones included on motherboards.
  • -1 Hide
    emperornicon , March 26, 2011 4:30 PM
    Take look at my motherboard it Gigabyte GA-MA790XT-U4DP even though it has sb600 South Bridge. I have a 1500 GB Raid-0 array it handles well at 631.3 MB/sec average write 231.6 MB/sec average. I found the balance between performances, capacity, and price. I noticed 4* 1 Tb Raid-0 drives with a 64mb buffer all Seagate Sata II, which reads, at 112 Mb/Sec and at Raid-0 * 4 drives 353 Mb/sec theoretically a Raid-0 * 6 drives 559 Mb/sec. to me it seems slower and when a drive goes it more expensive and you have more data loss.
    The larger the drive the longer the time to complete a job example 500 GB folder 3h 30m Raid-0 * 4 TB drives or at 6 * 250 GB which 1 h 50m and that duplicating to an identical array each time
  • 0 Hide
    netsql , March 27, 2011 2:22 PM
    That would be a good article, which Mobo has best RAID speed (of the new 500mb/s SSDs)
  • 0 Hide
    MRFS , March 27, 2011 3:52 PM
    Is this reviewer setting up a future comparison of these results with the same number of SATA/6G SSDs?

    The bandwidth of each LSI 9280-24i4e RAID controller port is 6 Gb/s, but "each drive has a capacity of 100 GB, is based on SLC NAND flash, has a 3 Gb/s SATA interface."

    I didn't see this discrepancy mentioned (yet) in any of the Comments above: please correct me I am wrong.

    p.s. If no more than 8 x SSDs are needed, then a less expensive 6G RAID controller is a viable option e.g. Highpoint RocketRAID 2720. I would enjoy seeing the results obtained from the same tests, using the latter RAID controller and scaling 1-8 Sandforce SF-2000 series 6G SSDs.


    MRFS
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