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 speed is good but not 840 Pro level. Some of this can be due to the slower NAND as the queue depth of our random read test is only 3—with higher queue depths the difference between 840 and 840 Pro should be closer.

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

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

Random write speed is a bit odd as performance does not scale up with higher queue depths. Speculating on the cause is difficult, but if I had to guess I would say it's firmware related, not NAND this time. Samsung is most likely doing some very aggressive write combining and caching so it's easy to achieve the same level of performance regardless of queue depth.

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)

Samsung's read centric firmware approach with the 840 really shows off in our low queue depth sequential read test: there is no drive faster than it.

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

Sequential write is pretty poor compared to today's other 256GB SSDs but Samsung is only claiming 250MB/s so this shouldn't come as a surprise. The similarity between random and sequential write speed helps back up what we mentioned earlier: Samsung is likely being very aggressive with its write combining to make random IOs look very sequential.

The Samsung SSD 840 AS-SSD Incompressible Sequential Performance
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  • name99 - Tuesday, October 09, 2012 - link

    "I think Kristian should have made this all more clear because too many people don't bother to actually read stuff and just look at charts."

    Kristian is not the problem.
    There is a bizarre fraction of the world of tech "enthusiasts" who are convinced that every change in the world is a conspiracy to screw them over.

    These people have been obsessing about the supposed fragility of flash memory from day one. We have YEARS of real world experience with these devices but it means nothing to them. We haven't been screwed yet, but with TLC it's coming, I tell you.
    The same people spent years insisting that non-replacable batteries were a disaster waiting to happen.
    Fifteen years ago they were whining about the iMac not including a floppy drive, for the past few years they have been whining about recent computers not including an optical drive.
    A few weeks ago we saw the exact same thing regarding Apple's new Lightning connector.

    The thing you have to remember about these people is
    - evidence means NOTHING. you can tell them all the figures you want, about .1% failure rates, or minuscule return rates or whatever. None of that counts against their gut feeling that this won't work, or even better an anecdote that some guy some somewhere had a problem.
    - they have NO sense of history. Even if they lived through these transitions before, they cannot see how changes in 2000 are relevant to changes in 2012.
    - they will NEVER admit that they were wrong. The best you can possibly get out of them is a grudging acceptance that, yeah, Apple was right to get rid of floppy disks, but they did it too soon.

    In other words these are fools that are best ignored. They have zero knowledge of history, zero knowledge of the market, zero knowledge of the technology --- and the grandiose opinions that come from not actually knowing any pesky details or facts.
    Reply
  • piiman - Tuesday, February 19, 2013 - link

    Then stick with Intel not because they last longer but they have a great warranty.(5 years) My drive went bad at about 3.5 years and Intel replaced it no questions asked and did it very quickly. I sent it in and had a new one 2 days after they received my old one. great service! Reply
  • GTRagnarok - Monday, October 08, 2012 - link

    This is assuming a very exaggerated amplification of 10x. Reply
  • Kristian Vättö - Monday, October 08, 2012 - link

    Keep in mind that it's an estimation based on the example numbers. 10x write amplification is fairly high for consumer workloads, most usually have something between 1-3x (though it gets a big bigger when taking wear leveling efficiency into account). Either way, we played safe and used 10x.

    Furthermore, the reported P/E cycle counts are the minimums. You have to be conservative when doing endurance ratings because every single die you sell must be able to achieve that. Hence it's completely possible (and even likely) that TLC can do more than 1,000 P/E cycles. It may be 1,500 or 3,000, I don't know; but 1,000 is the minimum. There is a Samsung 830 at XtremeSystems (had to remove the link as our system thought it was spam, LOL) that has lasted for more than 3,000TiBs, which would translate to over 10,000 P/E cycles (supposedly, that NAND is rated at 3,000 cycles).

    Of course, as mentioned at the end of the review, the 840 is something you would recommend to a light user (think about your parents or grandparents for instance), whereas the 840 Pro is the drive for heavier users. Those users are not writing a lot (heck, they may not use their system for days!), hence the endurance is not an issue.
    Reply
  • A5 - Monday, October 08, 2012 - link

    Ah. I didn't know the 10x WA number was exceedingly conservative. Nevermind, then. Reply
  • TheinsanegamerN - Friday, July 05, 2013 - link

    3.5 years is considering you are writing 36.5 GB of data a day. if the computer it is sitting in is mostly used for online work of document editing, youll get far more. the laptop would probably die long before the ssd did.
    also, this only apples to the tls ssds. mlc ssds last 3 times longer, so the 840 pro would be better for a computer kept longer than 3 years.
    Reply
  • Vepsa - Monday, October 08, 2012 - link

    Might just be able to convince the wife that this is the way to go for her computer and my computer. Reply
  • CaedenV - Monday, October 08, 2012 - link

    That is how I did it. My wife's old 80GB system drive died a bit over a year ago, and it was one of those issues of $75 for a decent HDD, or $100 for an SSD that would be 'big enough' for her as a system drive (60GB at the time). So I spent the extra $25, and it made her ~5 year old Core2Duo machine faster (for day-to-day workloads) than my brand new i7 monster that I had just build (but was still using traditional HDD at the time).

    I eventually got so frustrated by the performance difference that I ended up finally getting one for myself, and then after my birthday came then I spent my fun money on a 2nd one for RAID0. It did not make a huge performance increase (I mean it was faster in benchmarks, but doubling the speed of instant is still instant lol), but it did allow me to have enough space to load all my programs on the SSD instead of being divided between the SSD and HDD.
    Reply
  • AndersLund - Sunday, November 25, 2012 - link

    Notice, that setting up a RAID with your SSD might hinder the OS to see the SSDs as SSD and not sending TRIM commands to the disks. My first (and current) gamer system consists of two Intel 80 GB SSD in a RAID0 setup, but the OS (and Intel's toolbox) does not recognize them as SSD. Reply
  • mayankleoboy1 - Monday, October 08, 2012 - link

    Samsung is known to release only a few firmware updates (unlike SF).
    But due to the somewhat quirky nature of TLC NAND, do you expect Samsung to release a newer firmware , with maybe better read performance , or better TRIM support ?
    Reply

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