One SSD Vs. Two In RAID: Which Is Better?

RAID 0: Great For Benchmarks, Not So Much In The Real World

They're a funny thing, SSD benchmarks. You can run synthetics all day long and create these unrealistically demanding workloads that make solid-state storage look one way. Then, you can tinker around with real-world metrics that paint another picture entirely.

For enthusiasts, the truth often lies somewhere in between. A majority of the tasks we perform do tend to involve basic operations like opening Web browsers, editing images, composing email, and watching video. But sometimes we do need big performance from our systems: compiling a big project, moving tens of gigabytes of media files, or capturing uncompressed AVIs for FCAT analysis. In those instances, you want responsiveness on demand.

As we expected, twin SSDs in RAID 0 post phenomenal numbers when we hammer them with sequential reads and writes. Twin 256 GB 840 Pros nearly hit 1 GB/s in both disciplines. Largely as a result of the SATA 6Gb/s interface, single drives max out at a little more than half of those numbers.

The RAID-based configurations undoubtedly scored the first touchdown given exceptional sequential results, but the game didn't end there. Individual SSDs regained ground in the tests that followed, even posting better scores in some of them. Random I/O performance is a good example. Striped drives are certainly better equipped to push more IOPS, but only when you're stacking commands more than four high. Jumping up to a queue depth of 32, 16, or even eight is really uncommon in a desktop or workstation environment. As a result, the performance differences are far less pronounced in the real world.

One SSD on its own scores again in the contrived tests we put together. The performance differences when we boot up and shut down Windows 8, then fire up different applications, are marginal at best and not noticeable in practice. Single drives actually manage to outperform the striped arrays some of the time, even.

If you're planning an upgrade and want to know whether to buy a couple of 128 GB drives and put them in RAID 0 or just grab a single 256 GB SSD, for example, the answer still seems clear enough to us: just grab the large drive and use one. Using Samsung's 840 Pros as an example, a pair of 128 GB drives will run you $300 on Newegg right now. The 256 GB model sells for $240 (maybe that's why it's out of stock currently). There's also the issue of reliability. If one drive in a RAID 0 configuration fails, the entire array is lost. At least for a primary system drive, one SSD on its own is safer.

There are of course exceptions. SATA 6Gb/s currently limits us to 500+ MB/s reads and sub-500 MB/s writes. Sometimes, that's just not enough. Just take those raw AVI captures mentioned earlier as an example. We use four Crucial m4s in RAID 0 to make sure we aren't dropping any frames. In a case like that, RAID 0 is a must-have, and the fact that only captured video resides on the array means that a failure would be a fairly superficial loss (except the cost of the drive). If you have an application like that, well, then you already know what you need, and you know that a large, single drive isn't going to get the job done.

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  • ipheegrl
    Use a workstation with 6x 256GB Samsung 840 Pros in RAID 0 on an LSI 9271-8iCC PCIe RAID controller.

    Pulls about ~100,000 IOPS on the IOMeter workstation benchmark pattern at high queue depths, so performance does scale as expected.

    KamabPutting them in RAID0 doubles your chance of data failure, aka either drive fails and you probably lose everything.


    Look at data for the returns rate for Samsung SSDs

    http://www.behardware.com/articles/881-7/components-returns-rates-7.html

    At 0.48%, the odds of at least one drive failing in even a six drive array are around 2.9%. Now compare that to HDD failure rates here:

    http://www.behardware.com/articles/881-6/components-returns-rates-7.html

    and it's in the same ballpark. Let's also not forget how differently HDD and SSD failure rates change with time:

    http://www.tomshardware.com/reviews/ssd-reliability-failure-rate,2923-9.html

    Samsung lists consumer AFR for the 840 Pro at 0.16%, but the real number is likely in between the two.

    IMO, the increase in failure rate is not really significant. I'm not saying you shouldn't keep backups of crucial data, I have an HDD RAID 1 array just for that purpose. But it's certainly not a deal breaker, especially with the performance it gives.

    Vorador2RAID0 considerably increases the wear and tear on the drives so they will fail earlier.


    This could only hold true for drives that use on-the-fly compression, like Sandforce SSDs. Samsung's in-house controller doesn't utilize on-the-fly compression. Moreover, given the same load, writes will be distributed across all drives in RAID 0 compared to being written to a single drive. So even if maximum wear scales linearly with drive capacity, you won't see any appreciable change in lifespan.

    Not to mention that for 256 GB MLC drives with 3000 P/E cycles, you have to write at least 700 TB before you get close to the limit. Given the caution most people have been told to have writing to SSDs, it's more likely you'll buy new drives before your old ones wear out.

    tsondoI am surprised that the article did not mention the biggest performance drawback of RAID0 with SSDs. TRIM is not supported for most RAID0 controllers. Over time, you are going to lose any performance advantage you initially had, at least with MLC. No one should use RAID0 with SSDs unless they can periodically delete everything and reset the drives. If you are using a recent Intel controller you may be ok, but it's worth checking before you invest in it.


    Garbage collection algorithms are a lot better than they were in the past. I'd agree with you if you were running a server under constant load, but if you give the drives some idle time, they'll recover. Just look at the review for the Samsung 840:

    http://www.anandtech.com/show/6337/samsung-ssd-840-250gb-review/11

    Some idle time restored write performance completely after torture tests.

    Unless you need large and sustained I/O, garbage collection will suffice.
    24
  • Xazax310
    You dont have to RAID 0 them just to get more storage it be safer just to have them seperate, as 500GB/500GB drives
    15
  • Kamab
    Putting them in RAID0 doubles your chance of data failure, aka either drive fails and you probably lose everything.
    11
  • Other Comments
  • pocketdrummer
    I just bought a Samsung 840 Pro 512Gb. I plan to buy another and RAID 0 them, but not for speed. I just want 1TB of storage on an SSD. I dual boot and have a ton of Pro Audio applications and games I'd like to load quickly. I know it's an absurd amount of money for storage, but it makes me happy.

    2nd kind of cool, right?
    -8
  • Kamab
    Putting them in RAID0 doubles your chance of data failure, aka either drive fails and you probably lose everything.
    11
  • Xazax310
    You dont have to RAID 0 them just to get more storage it be safer just to have them seperate, as 500GB/500GB drives
    15
  • JonnyDough
    What they're saying is that even large game file load times won't be cut much, if at all. RAID with high speed SSDs on a home system makes very little sense. Without a fast (and expensive) dedicated hardware RAID card there's pretty much ZERO point in doing raid for home use.
    2
  • slyu9213
    pocketdrummerI just bought a Samsung 840 Pro 512Gb. I plan to buy another and RAID 0 them, but not for speed. I just want 1TB of storage on an SSD. I dual boot and have a ton of Pro Audio applications and games I'd like to load quickly. I know it's an absurd amount of money for storage, but it makes me happy.2nd kind of cool, right?


    If you don't care about the speed boost of RAID 0 I would suggest you not RAID 0 them but just use them separately as two 512GB drives. By doing this you have less risk of losing all of your data because your data won't be mixed through both drives.

    KamabPutting them in RAID0 doubles your chance of data failure, aka either drive fails and you probably lose everything.


    Which was already stated in the article/benchmark. Real world differences are too small, maybe even worse in half of the tests. One positive is for the raw video captures like at the end of the article.
    11
  • JackNaylorPE
    I don't see the "surprise". This has always been true of RAID 0....here's some oldies :)

    http://en.wikipedia.org/wiki/RAID_0#RAID_0

    RAID 0 is useful for setups such as large read-only NFS servers where mounting many disks is time-consuming or impossible and redundancy is irrelevant.

    RAID 0 is also used in some gaming systems where performance is desired and data integrity is not very important. However, real-world tests with games have shown that RAID-0 performance gains are minimal, although some desktop applications will benefit.[1][2]


    http://www.anandtech.com/printarticle.aspx?i=2101
    "We were hoping to see some sort of performance increase in the game loading tests, but the RAID array didn't give us that. While the scores put the RAID-0 array slightly slower than the single drive Raptor II, you should also remember that these scores are timed by hand and thus, we're dealing within normal variations in the "benchmark".

    Our Unreal Tournament 2004 test uses the full version of the game and leaves all settings on defaults. After launching the game, we select Instant Action from the menu, choose Assault mode and select the Robot Factory level. The stop watch timer is started right after the Play button is clicked, and stopped when the loading screen disappears. The test is repeated three times with the final score reported being an average of the three. In order to avoid the effects of caching, we reboot between runs. All times are reported in seconds; lower scores, obviously, being better. In Unreal Tournament, we're left with exactly no performance improvement, thanks to RAID-0

    If you haven't gotten the hint by now, we'll spell it out for you: there is no place, and no need for a RAID-0 array on a desktop computer. The real world performance increases are negligible at best and the reduction in reliability, thanks to a halving of the mean time between failure, makes RAID-0 far from worth it on the desktop.

    Bottom line: RAID-0 arrays will win you just about any benchmark, but they'll deliver virtually nothing more than that for real world desktop performance. That's just the cold hard truth."


    http://www.techwarelabs.com/articles/hardware/raid-and-gaming/index_6.shtml
    ".....we did not see an increase in FPS through its use. Load times for levels and games was significantly reduced utilizing the Raid controller and array. As we stated we do not expect that the majority of gamers are willing to purchase greater than 4 drives and a controller for this kind of setup. While onboard Raid is an option available to many users you should be aware that using onboard Raid will mean the consumption of CPU time for this task and thus a reduction in performance that may actually lead to worse FPS. An add-on controller will always be the best option until they integrate discreet Raid controllers with their own memory into consumer level motherboards."

    http://www.hardforum.com/showthread.php?t=1001325
    "However, many have tried to justify/overlook those shortcomings by simply saying "It's faster." Anyone who does this is wrong, wasting their money, and buying into hype. Nothing more."

    http://jeff-sue.suite101.com/how-raid-storage-improves-performance-a101975
    "The real-world performance benefits possible in a single-user PC situation is not a given for most people, because the benefits rely on multiple independent, simultaneous requests. One person running most desktop applications may not see a big payback in performance because they are not written to do asynchronous I/O to disks. Understanding this can help avoid disappointment."

    http://www.scs-myung.com/v2/index. [...] om_content
    "What about performance? This, we suspect, is the primary reason why so many users doggedly pursue the RAID 0 "holy grail." This inevitably leads to dissapointment by those that notice little or no performance gain.....As stated above, first person shooters rarely benefit from RAID 0.__ Frame rates will almost certainly not improve, as they are determined by your video card and processor above all else. In fact, theoretically your FPS frame rate may decrease, since many low-cost RAID controllers (anything made by Highpoint at the tiem of this writing, and most cards from Promise) implement RAID in software, so the process of splitting and combining data across your drives is done by your CPU, which could better be utilized by your game. That said, the CPU overhead of RAID0 is minimal on high-performance processors."
    10
  • JonnyDough
    It made more sense with hard drives when they were very slow. Overall I felt I noticed slightly reduced overall system performance on socket 939 back in the day with my dual raptor drives, however larger game save files (ie Oblivion) seemed to see a slight reduction in overall load times.
    2
  • Matsushima
    Would also have liked to seen storage controller benchmarks like motherboard chipsets vs specialised RAID controllers. I remember Tom's did an article on RAID controllers and migration back in 2005. DFI had not quit the enthusiast market back then.
    4
  • JonnyDough
    Although dedicated RAID controllers might change this a bit, when you consider that software raid on a modern high end CPU will use very little of the overall CPU power, I'm not sure it would make much difference if any.
    3
  • jase240
    I understand RAID0 is more dangerous, but I myself plan on using 2x 256GB in RAID0 soon. The speed gains might not be there in applications but right now 2 256GB drives are cheaper than 1 512GB drive on newegg.com, $479.98 vs $499.99.

    And as far as data loss in case of failure, don't use an SSD to store you data, use a separate HDD to store any important data(I have a 2TB drive).
    However it all comes to opinion, some users don't want to worry about RAID nor take the time to setup(I don't blame them either).
    0
  • cats_Paw
    Funny how ive been trying to explain this over and over to people who dont belive it >:D.
    0
  • zivgt2
    What if I have several old and small capacity HDD and a old computer, is it still useless to use RAID0 on them?
    0
  • Vorador2
    From my experience:

    For your workstation, buy a single SSD and regularly do backups of important data. RAID0 is fast, but not only the failure of a single drive will make all data irrecoverable, but also RAID0 considerably increases the wear and tear on the drives so they will fail earlier. If you've got money to burn, buy a quality SSD. For standard use, it's more than enough.

    For servers, RAID makes far more sense since time is money, and for every minute of downtime, money is lost.
    0
  • kronos_cornelius
    Just get a PCIe SSD... why bother with SATA anymore ?
    2
  • Marcus52
    KamabPutting them in RAID0 doubles your chance of data failure, aka either drive fails and you probably lose everything.


    Yes, but the actual MTBF of SSDs is so high that I personally consider it to be a moot point. Not that it isn't valid for someone running their business, but my use means failure is more a matter of convenience than lost income.

    Seems to me the answer is, as always, application dependent. Most of us gamer-types aren't going to benefit from a RAID 0 configuration, but if you build using one, the down sides are very low, and the potential upside, if you happen to expand beyond gaming and use an app that takes advantage of it, is very high. That being said, price is a big factor for me, and there just isn't any reason to pay $300 instead of $240, to use the example in the article, when I'm not likely to ever actually run apps that take advantage of the higher limit using 2 SATA connections allows for.
    0
  • Marcus52
    Oh, I meant to say - thanks for the article guys, it is always good to have theories confirmed (or not) by good testing, and this directly relates to my next build.
    0
  • rolli59
    Great article and we stick to the recommendation of buying the largest SSD you can afford.
    0
  • tsondo
    I am surprised that the article did not mention the biggest performance drawback of RAID0 with SSDs. TRIM is not supported for most RAID0 controllers. Over time, you are going to lose any performance advantage you initially had, at least with MLC. No one should use RAID0 with SSDs unless they can periodically delete everything and reset the drives. If you are using a recent Intel controller you may be ok, but it's worth checking before you invest in it.
    2
  • TheBigTroll
    yet people still want raid 0 SSDs.
    1
  • NeeKo
    If you dont want to lose any data with a RAID of SSDs then make a RAID1+0 : P ?

    Boy that would be costly
    0