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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  • Kevin G - Monday, October 08, 2012 - link

    On the fourth page:

    "With perfect wear-leveling and write amplification of 1x, you would get 256TiB of writes out of a 250GB Samsung 840 with TLC NAND and 1,000 P/E cycles. "

    Shouldn't it be 256 GiB?
    Reply
  • JarredWalton - Monday, October 08, 2012 - link

    No; he's accounting for the visible storage capacity (and spare area). So 250GB is 256GiB of NAND but only 250GB end-user storage. You can still write 256TiB of data (256GiB * 1000 P/E), which means on a 250GB SSD you end up with the ability to write 281TB of data (for an effective P/E cycles of 1125). Reply
  • schizoide - Monday, October 08, 2012 - link

    I'm not comfortable with TLC, particularly since it doesn't come at a huge absolute cost savings. I've been burned too often with SSDs, and now only buy the most bulletproof devices available. Maybe next generation. Maybe. Reply
  • Death666Angel - Tuesday, October 09, 2012 - link

    I wouldn't draw any conclusion for pricing just yet. Everyone is comparing street prices of current gen SSDs to MSRP of next gen SSDs. Give it a few months to get the 840 into stores and selling and then we'll se how prices fair.
    I'm personally fairly confident that there will be a distinct cost advantage.
    Reply
  • name99 - Tuesday, October 09, 2012 - link

    Have ANY SSDs given you a failure based on the flash cells themselves, rather than on crappy firmware?
    It's stupid to demonize a technology because some companies sold you a bad product --- especially when your response is to refuse to buy a product from a company that is known (in this respect at least) NOT to have shipped crappy firmware.
    Reply
  • harijan - Monday, October 08, 2012 - link

    Pretty sure 3650GiB != 3.65TiB.

    3650GB == 3.65TB.

    It doesn't do anything to your percentages, but this is Anandtech, we hold you to higher standards ;)
    Reply
  • Kristian Vättö - Tuesday, October 09, 2012 - link

    You are correct, I forgot that binary units don't scale up linearly (1000GiB is not 1TiB); metrics are just so much simpler. Thanks for the heads up, I've fixed the math now. Reply
  • iaco - Monday, October 08, 2012 - link

    I wonder if Samsung will ever make a SSD made of SLC NAND. The performance would be amazing. Reply
  • Conficio - Monday, October 08, 2012 - link

    First thanks to the Kristan and the Anand Team for another comprehensive review and the inclusion of in depth knowledge about the technology behind it.

    I'd like to see included in the test (or in another article) a review of the available tools for each SSD. I think it is important to know if the manufacturer supports its tools to low level format, secure erase, TRIM, ROM update etc. beyond the obligatory Windows (7). Are those available for Linux (command line and/or GUI)? Are they available for Mac OSX? Do they work if the drive is connected over USB? Are these tools user friendly to use?

    It is useless if I buy an SSD and have to find out that Mac OSX does not support the tools. I have a couple of Vertex drives which I can't find a way to secure erase in order to restore full performance. They are pre TRIM drives and Mac OS X does not support trim on them anyway.

    As with motherboards, the the BIOS or UEFI is important, so is with SSDs the ability to actually perform some of the low level functions. I hope you can add that to your workload! A comparison of the different tools for each manufacturer for current drives would be a great start. Thanks again!
    Reply
  • Kristian Vättö - Tuesday, October 09, 2012 - link

    Samsung will be releasing Magician 4.0 later this year and we are definitely going to do an article about it. I tried to get a beta version of it but Samsung wasn't willing to send us one, yet. Magician 3.2.2 that comes with the 840 is the same that's available for the 830, so I didn't find it that important to cover.

    But you are right, we need to cover the software side more as well because it will also drive manufacturers to make their own SSD tools.

    P.S. Try installing Ubuntu to a USB stick (just use UNetBootin) and then use hdparm commands (see below) to secure erase the SSD.

    sudo hdparm --user-master u --security-set-pass password /dev/sdX

    sudo hdparm --user-master u --security-erase password /dev/sdX

    "password" is whatever you choose as the password and "X" is the drive (you can see which it is in Disk Utility)
    Reply

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