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.

Desktop Iometer - 4KB Random Read (4K Aligned)

Random read performance has never been SandForce's biggest strength and even Intel couldn't massively improve it with its own firmware. The SSD 335 is in fact slower than the SSD 330 here.

Desktop Iometer - 4KB Random Write (4K Aligned) - 8GB LBA Space

Desktop Iometer - 4KB Random Write (8GB LBA Space QD=32)

Random write speed at small queue depths is also slower compared to the 520 and 330, although at queue depth of 32 the difference is negligible. 

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.

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

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

Sequential read performance is identical to SSD 330, but sequential write speed is slightly slower. What's notable is sequential write performance with incompressible data: the Intel SSD 335 manages to beat both the 520 and Corsair's Force GS by a noticeable margin.

Inside the Intel SSD 335 and Test Setup AS-SSD Incompressible Sequential Performance
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  • Per Hansson - Tuesday, October 30, 2012 - link

    No, it does not work like that.
    A slow DMM might take a reading every second.
    An example, in seconds:
    1: 2w
    2: 2w
    3: 2w
    Average=2w

    A fast DMM might take readings every 100ms:
    1: 2w
    2: 0.5w
    3: 2w
    4: 0.5w
    Average=1w

    As you see a DMM does not take a continous reading, it takes readings at points in time and averages those...

    An SSD drive might actually change power levels much more frequently, like every millisencond (consider their performance, how long does it take to write 4KB of data as an example?)
    Reply
  • hrga - Thursday, November 01, 2012 - link

    dont think SSD even try to write such a small amount of data as 4kB every milisecond considering how large buffers usually have 128GB LPDDR2. So thes kind of small writes occur in bursts when they accumulate every 15-30s (at least hope so as this was case with hard drives) That ofc depends on firmware and values in it. Reply
  • Per Hansson - Thursday, November 01, 2012 - link

    That makes no difference, I sincerely hope that no drive waits 15 > 30 seconds to write data to disk because that is just a recipe for data loss in case of power failure or BSOD.
    I also hope no drive uses a 128GB write cache. (Intel's in house controller keeps no user data in cache as an example, but I digress)

    Even if the drive waits a minute before it writes the 4KB of data you must still have a DMM capable of catching that write, which is completed in less than a millisecond.
    Otherwise the increased power consumption during the disk write will be completely missed by the DMM
    Reply
  • Mr Alpha - Monday, October 29, 2012 - link

    Wouldn't it make more sense to the idle power consumption on a platform that supports DPIM? The idle power usage is mostly a matter on mobile devices, and it is on those you get DPIM support. Reply
  • sheh - Monday, October 29, 2012 - link

    The text says total writes were 1.2TB, (+3.8TB=) 5TB, and 37.8TB. The screenshots show "host writes" at 1.51TB, 2.11TB, and 3.90TB? Reply
  • sheh - Monday, October 29, 2012 - link

    And why the odd power on hours counts? Reply
  • Kristian Vättö - Monday, October 29, 2012 - link

    You are mixing host writes with the actual NAND writes. Host writes are the data that the host (e.g. an operating system) sends to the SSD controller to write. NAND writes show much is written to the NAND.

    When the SSD is pushed to a corner like I did, you will end up having more NAND writes than host writes because of read-modify-write (i.e. all user-accessible LBAs are already full, so the controller must read the block to a cache, modify the data and rewrite the block). Basically, your host may be telling the controller to write 4KB but the controller ends up writing 2048MB (that's the block size).
    Reply
  • extide - Monday, October 29, 2012 - link

    Block size is 2048KB* Reply
  • sheh - Monday, October 29, 2012 - link

    So the write amplification in the end was x9.7?

    Are NAND writes also reported by SMART?

    And with the messed up power on count, how can you know the rest of the SMART data is reliable?
    Reply
  • Kristian Vättö - Tuesday, October 30, 2012 - link

    Yes, write amplification was around 9.7x in the end. That makes sense because the drive becomes more and more fragmented the more you write to it.

    As you can see in the screenshots, the SMAT value F9 corresponds to NAND writes. Most manufacturers don't report this data, though.

    We just have to assume that the values are correct. Otherwise we could doubt every single test result we get, which would make reviewing impossible. The data makes sense so at least it's not screaming that something is off, and from what I have read, we aren't the only site who noticed weird endurance behavior.
    Reply

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