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.

As impressive as the random read/write speeds were, at low queue depths the Vertex 4's sequential read speed is problematic:

Desktop Iometer - 128KB Sequential Read (4K Aligned)

Curious as to what's going on, I ran AS-SSD and came away with much better results:

Incompressible Sequential Read Performance - AS-SSD

Finally I turn to ATTO, giving me the answer I'm looking for. The Vertex 4's sequential read speed is slow at low queue depths with certain workloads, move to larger transfer sizes or high queue depths and the problem resolves itself:

QD2
QD4
QD8

The problem is that many sequential read operations for client workloads occur at 64 – 128KB transfer sizes, and at a queue depth of 1 - 3. Looking at the ATTO data above you'll see that this is exactly the weak point of the Vertex 4.

I went back to Iometer and varied queue depth with our 128KB sequential read test and got a good characterization of the Vertex 4's large block, sequential read performance:

The Vertex 4 performs better with heavier workloads. While other drives extract enough parallelism to deliver fairly high performance with only a single IO in the queue, the Vertex 4 needs 2 or more for large block sequential reads. Heavier read workloads do wonderfully on the drive, ironically enough it's the lighter workloads that are a problem. It's the exact opposite of what we're used to seeing. As this seemed like a bit of an oversight, I presented OCZ with my data and got some clarification.

Everest 2 was optimized primarily for non-light workloads where higher queuing is to be expected. Extending performance gains to lower queue depths is indeed possible (the Everest 1 based Octane obviously does fine here) but it wasn't deemed a priority for the initial firmware release. OCZ instead felt it was far more important to have a high-end alternative to SandForce in its lineup. Given that we're still seeing some isolated issues on non-Intel SF-2281 drives, the sense of urgency does make sense.

There are two causes for the lower than expected, low queue depth sequential read performance. First, OCZ doesn't currently enable NCQ streaming for queue depths less than 3. This one is a simple fix. Secondly, the Everest 2 doesn't currently allow pipelined read access from more than 8 concurrent NAND die. For larger transfers and queue depths this isn't an issue, but smaller transfers and lower queue depths end up delivering much lower than expected performance.

To confirm that I wasn't crazy and the Vertex 4 was capable of high, real-world sequential read speeds I created a simple test. I took a 3GB archive and copied it from the Vertex 4 to a RAM drive (to eliminate any write speed bottlenecks). The Vertex 4's performance was very good:

Sequential Read - 3GB Archive Copy to RAM Disk

Clearly the Vertex 4 is capable of reading at very high rates – particularly when it matters, however the current firmware doesn't seem tuned for any sort of low queue depth operation.

Both of these issues are apparently being worked on at the time of publication and should be rolled into the next firmware release for the drive (due out sometime in late April). Again, OCZ's aim was to deliver a high-end drive that could be offered as an alternative to the Vertex 3 as quickly as possible.

Update: Many have been reporting that the Vertex 4's performance is dependent on having an active partition on the drive due to its NCQ streaming support. While this is true, it's not the reason you'll see gains in synthetic tests like Iometer. If you don't fill the drive with valid data before conducting read tests, the Vertex 4 returns lower performance numbers. Running Iometer on a live partition requires that the drive is first filled with data before the benchmark runs, similar to what we do for our Iometer read tests anyway. The chart below shows the difference in performance between running an Iometer sequential read test on a physical disk (no partition), an NTFS partition on the same drive and finally the physical disk after all LBAs have been written to:

Notice how the NTFS and RAW+precondition lines are identical, it's because the reason for the performance gain here isn't NCQ streaming but rather the presence of valid data that you're reading back. Most SSDs tend to give unrealistically high performance numbers if you read from them immediately following a secure erase so we always precondition our drives before running Iometer. The Vertex 4 just happens to do the opposite, but this has no bearing on real world performance as you'll always be reading actual files in actual use.

Despite the shortcomings with low queue depth sequential read performance, the Vertex 4 dominated our sequential write tests, even at low queue depths. Only the Samsung SSD 830 is able to compete:

Desktop Iometer - 128KB Sequential Write (4K Aligned)

Technically the SF-2281 drives equal the Vertex 4's performance, but that's only with highly compressible data. Large sequential writes are very often composed of already compressed data, which makes the real world performance advantage of the Vertex 4 tangible.

Incompressible Sequential Write Performance - AS-SSD

AS-SSD gives us another taste of the performance of incompressible data, which again is very good on the Vertex 4. As far as writes are concerned, there's really no beating the Vertex 4.

Random Read/Write Speed AnandTech Storage Bench 2011
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  • ViviTheMage - Wednesday, April 04, 2012 - link

    mmmmmm, iops. Reply
  • LB-ID - Wednesday, April 04, 2012 - link

    It's still a drive from OCZ, a company that has repeatedly and blatantly used its customer base as unpaid beta testers, and lambasted them when they dared to complain about it. No thank you. The fastest drive in the world is of no use to me if it's causing my computer to BSOD constantly. I'll be spending my money and that of my many clients on drives with proven track records for reliability and excellent customer service, both sadly lacking in OCZ products. Reply
  • hackztor - Wednesday, April 04, 2012 - link

    Ocz is the only one that actually got to the bottom of the bsod screen on sandforce. In the end it was sandforce fault because they made the controller. All the other companies waited and then used the fix. Intel is the exception who waited a whole year before releasing them to validate but they still use sandforce controllers. Vertex4 is the 1st time that ocz now owns the controller and firmware that goes into the product. I hope this will prove to be better and have quicker fixes. Ocz is always the first to release the technology so expect some issues, but thats what people take for early adopting. I had 5 vertex 1 die on me and then they upgraded me to a vertex2. Just purchased the 4 so hope all goes well. Reply
  • taltamir - Wednesday, April 04, 2012 - link

    "Ocz is the only one that actually got to the bottom of the bsod screen on sandforce."

    Actually that was intel.
    Reply
  • hackztor - Wednesday, April 04, 2012 - link

    Not true. Ocz pushed sandforce to finally find the issue based on what the users were telling ocz while sandforce kept trying to deny the issue and could not find it in a lab environment. If you see further down I said intel waited a year with validation going on. Reply
  • breakSSD - Thursday, April 05, 2012 - link

    You have no idea about ssd validation if you think Ocz pushed sandforce for BSOD.The fact is that Intel found this and kept sandforce busy with fixing the issue while ocz even though knowing the issue release agility 3. Anyways doesn't matter who takes the credit, people know where to go when it comes to reliability. Reply
  • iceman98343 - Friday, April 06, 2012 - link

    you do realize intel 520s are now getting bsods?! Reply
  • Obsoleet - Saturday, April 07, 2012 - link

    You go to Samsung for reliability. Iceman is correct, word is spreading of more 520 stability issues. If you want the fastest, most reliable SSD get the 830 as Anand recommends. Reply
  • Einy0 - Saturday, April 07, 2012 - link

    At work we have deployed about 50 - 80GB Intel 320 Series Drives and so far nearly 60 - 64GB Samsung 830 Drives. The Samsung drives are screamers but we've seen a lot of strange issues with the Samsung drives that we never had with the Intel drives. We have not had a single drive from either company fail or come DOA. That amazes me personally, not a single dud. We've literally had dozens of faculty members come ask us what we did to their computer that made it so fast all of a sudden. The issues we've had with the Samsung drives about 1 in 10 causes Windows mini-setup to freeze. We re-image the drive again it works just fine. We are thinking maybe the compatibility with some SATA controllers isn't as robust on the Samsung drives as it is on the Intel drives. Reply
  • gandx - Tuesday, April 24, 2012 - link

    Or choose a SSD with a marvell controller like the Corsair Performance Pro or Plextor M3P. Both are fast and stable. I would never choose a SSD with sandforce again after using a vertex 3 for a while with lot or problems and i'm obviously not the only one. Reply

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