Random Read/Write Speed

The four corners of SSD performance are as follows: random read, random write, sequential read and sequential write speed. Random accesses are generally small in size, while sequential accesses tend to be larger and thus we have the four Iometer tests we use in all of our reviews.

Our first test writes 4KB in a completely random pattern over an 8GB space of the drive to simulate the sort of random access that you'd see on an OS drive (even this is more stressful than a normal desktop user would see). I perform three concurrent IOs and run the test for 3 minutes. The results reported are in average MB/s over the entire time. We use both standard pseudo randomly generated data for each write as well as fully random data to show you both the maximum and minimum performance offered by SandForce based drives in these tests. The average performance of SF drives will likely be somewhere in between the two values for each drive you see in the graphs. For an understanding of why this matters, read our original SandForce article.

Iometer - 4KB Random Write, 8GB LBA Space, QD=3

Peak performance on the 120GB Vertex 3 is just as impressive as the 240GB pre-production sample as well as the m4 we just tested. Write incompressible data and you'll see the downside to having fewer active die, the 120GB drive now delivers 84% of the performance of the 240GB drive. In 3Gbps mode the 240 and 120GB drives are identical.

Many of you have asked for random write performance at higher queue depths. What I have below is our 4KB random write test performed at a queue depth of 32 instead of 3. While the vast majority of desktop usage models experience queue depths of 0 - 5, higher depths are possible in heavy I/O (and multi-user) workloads:

Iometer - 4KB Random Write, 8GB LBA Space, QD=32

At high queue depths the gap between the 120 and 240GB Vertex 3s grows a little bit when we're looking at incompressible data.

Iometer - 4KB Random Read, QD=3

Random read performance is what suffered the most with the transition from 240GB to 120GB. The 120GB Vertex 3 is slower than the 120GB Corsair Force F120 (SF-1200, similar to the Vertex 2) in our random read test. The Vertex 3 is actually about the same speed as the old Indilinx based Nova V128 here. I'm curious to see how this plays out in our real world tests.

Sequential Read/Write Speed

To measure sequential performance I ran a 1 minute long 128KB sequential test over the entire span of the drive at a queue depth of 1. The results reported are in average MB/s over the entire test length.

Iometer - 128KB Sequential Write

Highly compressible sequential write speed is identical to the 240GB drive, but use incompressible data and the picture changes dramatically. The 120GB has far fewer NAND die to write to in parallel and in this case manages 76% of the performance of the 240GB drive.

Iometer - 128KB Sequential Read

Sequential read speed is also lower than the 240GB drive. Compared to the SF-1200 drives there's still a big improvement as long as you've got a 6Gbps controller.

The Vertex 3 120GB AnandTech Storage Bench 2011


View All Comments

  • sethm1 - Thursday, April 07, 2011 - link

    I was looking forward to the Vertex 3 as being the next best thing.
    And so was hoping for a more positive review (but yes appreciate the candor in the review).
    My question is, after all is said and done, is the Vertex 3 still better than the Vertex 2 (120GB versions)?
    Should I go out and get a version 2?
  • kmmatney - Thursday, April 07, 2011 - link

    The answer is pretty easy, I think. Anand's own storage bench is a great test of real world performance, especially the "typical workload"


    The bottom line: Version 3 is better than Verion 2, although not by an amazing amount
  • sunbear - Thursday, April 07, 2011 - link

    "3) Finally, are you willing to commit, publicly and within a reasonable period of time, to exchanging any already purchased product for a different configuration should our readers be unhappy with what they've got?"

    The problem is that it is not straight forward for a customer to know "what they've got" without opening up the SSD and voiding their warranty. OCZ provides the "OCZ Toolbox" that tells you whether your SSD contains 32Gb or 64Gb NAND chips but they don't currently provide any too; to determine whether you have the dreaded Hynix flash or the superior IMFT flash.

    I asked in the OCZ forum and their response was to do a secure erase and run the AS SSD benchmark. I have no idea what numbers from the AS SSD benchmark would indicate Hynix versus IMFT.
  • cptcolo - Friday, April 08, 2011 - link

    Hats off to both Anand and OCZ for fixing the Vertex 2 issue. I am really impressed by both Anand and Alex Mei. Anand thanks fo rbeing proactive and presenting OCZ with the problem, and thanks to Alex Mei and Ryan for taking care of the problem 100% (via the change in name and SKUs). You are both true alturists. Reply
  • B0GiE - Friday, April 08, 2011 - link

    I just cancelled my order of the 120Gb OCZ Vertex. It says on Scan webpage that it is 550mbs Read and 500mbs Write.

    Due to this review i'm not sure i believe it. I will wait for further reviews before I purchase a new SSD.

    I am interested in game load times for the Vertex 3 such as Black Ops but Anandtech does not show any???
  • gietrzy - Friday, April 08, 2011 - link

    I've just cancelled 120GB Vertex 3 drive. I have no time to investigate whether or not my drive performs as promised.
    I also have a Vertex 2 60 GB I think "E" version - how do I check if it's faulty.

    My scenario is #2 at this page http://www.anandtech.com/show/4256/the-ocz-vertex-...
    I also have lots of 1080p avchd videos and even more raw files from my camera so I think I will wait for Intel 510 120 GB review and buy Intel.

    One thing's for sure: I will never buy OCZ again.

    Thanks Anand, thanks guys!
  • mattcpa - Friday, April 08, 2011 - link

    I ordered the 120GB Vertex 3 from Computers4Sure on the morning before you published this review... :(
    I also picked up an HDD Optical Bay to put my MBPro 750GB HDD there and plan to put the 120GB in the 6gbps SATA.
    I use the Macbook Pro 15" 2.2 SBP for laptop DJ work along with handbraking movies and such; sprinkle in some random gaming.

    Hopefully for these processes, it appears this drive will still be near the top of the pack in terms of performance, as I feel I perform many read functions daily rather than performing constant writes. If someone has an opinion, let me know if I am wrong...
  • DLeRium - Friday, April 08, 2011 - link

    Come on. You HAVE to compare against last generation's Vertex 2. It's selling for $169 at Newegg, and you don't even bench against that. Sigh. Like it's fine if you miss out on some of the other ways say the Kingston, but to skip on the Vertex 2 is a major /facepalm. Reply
  • Shark321 - Friday, April 08, 2011 - link

    Yes, Vertex 2 and Agility 2 benchmarks compared to Vertex 3 would be really helpful here. Reply
  • db808 - Friday, April 08, 2011 - link

    Hi Anand,

    First, let me join in with the others in complementing you on your excellent article.

    I saw some interesting data hidden in the information describing the IO access patterns of your new IO benchmarks. I was very surprised that the IO size was so small, and that you mentioned that a majority of the IO was sequential.

    Some of this can be explained by the multi-threaded nature of the tests. Two applications, each doing sequential IO, running against each other, result in interleaved IOs going to the disk, with a result that is very non-sequential. Some of this may be explained by the application runtime actually requesting 4kb IO, and Windows not having time to do "read aheads".

    Windows does have the capability to do larger-IO than was requested by the application (opportunistic IOs), as well as read-ahead and write behinds(that are often coalesced into larger IOs) ... but SSDs may actually be so fast, that the Windows IO optimization algorithms don't have enough time to "think".

    You also pointed out that SSD IO performance increases very quickly has the IO size increases above 4kb. It appears that most of the modern controllers parallel stripe the IO across multiple channels, wear-leveling notwithstanding. So an 8kb IO is 2 parallel 4kb IO, for example (ignoring SandForce compression behavior).

    The simplest way to cajole the large share of 4kb IO's to 8kb or larger sizes is to simply increase the NTFS cluster size. This has been a performance optimization techniques used with high performance storage arrays for many years. Many Unix systems actually default to 8kb or larger block sizes, and EMC internally uses a 32kb block size as examples.

    There is a small negative tradeoff ... some additional slack space at the end of every file. The average slack space per file is 1/2 the cluster size, or 2kb for the default 4kb cluster. Increasing the cluster to 8kb, increases the slack space to 4kb per file ... for a 64kb cluster, it would be 32kb slack per file. The JAM Software "Treesize" utility will actually compute the total slack space for you. With TreeSize Pro, you can even do "what if" analysis and see the impact of changing the cluster size on total slack space.

    In summary, slack space overhead only represent a few percentage points of the disk capacity. For example, on my business laptop, by C: drive has about 262K files, and my total wasted space is ~ 644 MB. Increasing the cluster size to 8kb would roughly double my wasted space ... an additional 644MB. Not much.

    On my hard-disk based systems that are also memory rich, I regularly run NTFS cluster sizes of 8kb and 16kb ... 64kb for temp file systems. I am pro-actively trading a few percentage points of disk space for higher performance levels. The cost of a few GB of extra overhead on a 1TB disk is a no brainer.

    But SSDs are a lot more expensive, and space is a lot tighter. I use a SSD as a boot disk on one PC, and I've filled it about 1/2 full, with the OS, applications, page, hibernate, and temps. Performance is great, and the 40%-ish free space is a form of over-provisioning.

    My performance was so good, I had not yet experimented with increasing my cluster size, because I was not able to quantify what the IO size profile looked like. Your IO size statistics from your IO storage benchmark was very enlightening as it shows the (unexpected) large amount of small IO.

    On Sandforce-based SSDs, the controller would compress away all the slack space at the end a file, since Windows pads the last cluster in a file with zeros. So with a larger cluster size, your file system would look fuller under Windows, but all the extra slack space would be compressed on the SSD ... with little detriment to the over-provisioning headroom.

    I know you are exceedingly busy, but it would be extremely interesting to be able to re-run your controlled test environment with the Anand IO Storage 2011 tests on systems that were built with different cluster sizes. I suspect that using a larger cluster size would improve performance on all SSDs, with SSDs with weaker performance showing the most relative gain. From what I have read, increasing the cluster size beyond 16kb (for Sandforce controllers) will have diminishing (but still positive) returns.

    Increasing a Windows 7 boot disk's cluster size from 4kb to 16 kb would increase the wasted space about 4-fold. On my system that would be less than 3GB. It could be a worthwhile trade for performance.

    Another reason to explore larger cluster sizes is the fact that the new 28nm Flash chips typically have page sizes of 8kb, not the smaller 4kb used in the 32/34 nm Flash chips. When Windows does 4kb IO on these new 28nm Flash SSDs, it is actually doing sub-page IO, causing the controller to perform a read/modify/write function, and increasing the write amplification effect. The impact would be similar to doing 2kb IO on the SSDs with 4kb page sizes.

    If you assume that the typical compression factor is 2:1 for Sandforce controllers, a 16kb NTFS cluster would often be compressed to fit in a single 8kb page ... sounds like a sweet spot.

    Using a larger cluster size, also decrease the amount of work needed to append to a file, as fewer clusters need to be allocated. The cluster size also defines the lower limit of contiguousness. This could be important on SSDs, since we normally don't run defrag utilities on SSDs, so we know that fragmentation will only get worse over time.

    I will point out that using larger cluster sizes may increase memory usage for the kernel buffer pool, and/or reduce the effective number of buffers for a buffer pool of a given size. I only recommend increasing cluster sizes on systems in a "memory rich" environment.

    Again, thank you for your excellent report. Exploring the impact of larger cluster sizes, especially on 28nm based SSDs could add an additional dimension to your analysis. 8kb and larger cluster sizes could further improve real-world SSD performance, and mask some of the performance drop from using the 28nm chips.


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