Performance Consistency

In our Intel SSD DC S3700 review I introduced a new method of characterizing performance: looking at the latency of individual operations over time. The S3700 promised a level of performance consistency that was unmatched in the industry, and as a result needed some additional testing to show that. The reason we don't have consistent IO latency with SSDs is because inevitably all controllers have to do some amount of defragmentation or garbage collection in order to continue operating at high speeds. When and how an SSD decides to run its defrag and cleanup routines directly impacts the user experience. Frequent (borderline aggressive) cleanup generally results in more stable performance, while delaying that can result in higher peak performance at the expense of much lower worst case performance. The graphs below tell us a lot about the architecture of these SSDs and how they handle internal defragmentation.

To generate the data below I took a freshly secure erased SSD and filled it with sequential data. This ensures that all user accessible LBAs have data associated with them. Next I kicked off a 4KB random write workload across all LBAs at a queue depth of 32 using incompressible data. I ran the test for just over half an hour, no where near what we run our steady state tests for but enough to give me a good look at drive behavior once all spare area filled up.

I recorded instantaneous IOPS every second for the duration of the test. I then plotted IOPS vs. time and generated the scatter plots below. Each set of graphs features the same scale. The first two sets use a log scale for easy comparison, while the last set of graphs uses a linear scale that tops out at 50K IOPS for better visualization of differences between drives.

The high level testing methodology remains unchanged from our S3700 review. Unlike in previous reviews however, I did vary the percentage of the drive that I filled/tested depending on the amount of spare area I was trying to simulate. The buttons are labeled with the advertised user capacity had the SSD vendor decided to use that specific amount of spare area. If you want to replicate this on your own all you need to do is create a partition smaller than the total capacity of the drive and leave the remaining space unused to simulate a larger amount of spare area. The partitioning step isn't absolutely necessary in every case but it's an easy way to make sure you never exceed your allocated spare area. It's a good idea to do this from the start (e.g. secure erase, partition, then install Windows), but if you are working backwards you can always create the spare area partition, format it to TRIM it, then delete the partition. Finally, this method of creating spare area works on the drives we've tested here but not all controllers may behave the same way.

The first set of graphs shows the performance data over the entire 2000 second test period. In these charts you'll notice an early period of very high performance followed by a sharp dropoff. What you're seeing in that case is the drive allocating new blocks from its spare area, then eventually using up all free blocks and having to perform a read-modify-write for all subsequent writes (write amplification goes up, performance goes down).

The second set of graphs zooms in to the beginning of steady state operation for the drive (t=1400s). The third set also looks at the beginning of steady state operation but on a linear performance scale. Click the buttons below each graph to switch source data.

  Corsair Neutron 240GB Crucial M500 960GB Samsung SSD 840 Pro 256GB Seagate 600 480GB Seagate 600 Pro 400GB
Default
25% Spare Area    

Now this is a bit surprising. I expected a tightly clustered group of IOs like we got with the LAMD based Corsair Neutron, but instead we see something different entirely. There's a clustering of IOs around the absolute minimum performance, but it looks like the controller is constantly striving for better performance. If there's any indication that Seagate's firmware is obviously different than what Corsair uses, this is it. If we look at the 400GB Seagate 600 Pro we get a good feel for what happens with further over provisioning. The 400GB Pro maintains consistently high performance for longer than the 480GB 600, and when it falls off the minimums are also higher as you'd expect.

  Corsair Neutron 240GB Crucial M500 960GB Samsung SSD 840 Pro 256GB Seagate 600 480GB Seagate 600 Pro 400GB
Default
25% Spare Area    

Zooming in, the Seagate 600 definitely doesn't look bad - it's far better than the Samsung or Crucial offerings, but still obviously short of Corsair's Neutron. I almost wonder if Seagate prioritized peak performance a bit here in order to be more competitive in most client benchmarks.

  Corsair Neutron 240GB Crucial M500 960GB Samsung SSD 840 Pro 256GB Seagate 600 480GB Seagate 600 Pro 400GB
Default
25% Spare Area    

The situation really looks a lot worse than it is here. The 600's performance isn't very consistent, but there's a clear floor at just above 5000 IOPS which is quite respectable. Compared to the Crucial and Samsung drives, the 600/600 Pro offer much better performance consistency. I do wish that Seagate had managed to deliver even more consistent performance given that we know what the controller is capable of. For client usage I suspect this won't matter, but in random write heavy enterprise workloads with large RAID arrays it isn't desirable behavior.

The Seagate 600 & 600 Pro AnandTech Storage Bench 2013 Preview
POST A COMMENT

59 Comments

View All Comments

  • numberoneoppa - Tuesday, May 7, 2013 - link

    It's too bad about the idle power consumption, but if the prices are decent, I might pick up a higher capacity variant to replace my 80GB m25 G2 in my desktop. Reply
  • ssj3gohan - Tuesday, May 7, 2013 - link

    I don't think Anandtech has implemented their improved (DIPM-enabled) power consumption tests yet, so the idle figures here are pretty much meaningless. When it comes to market, check the datasheet for actual idle power consumption. Reply
  • Kristian Vättö - Tuesday, May 7, 2013 - link

    Seagate's datasheet shows average idle power of 1.1W: http://images.anandtech.com/doci/6935/Screen%20Sho... Reply
  • lightsout565 - Wednesday, May 8, 2013 - link

    Does anyone know how power consumption compares to the 128GB Samsung 830? In Anand's review of the 830 he mentions, "Samsung sampled the 512GB version of the SSD 830 so it's unclear how much the sheer number of NAND die impacts power consumption here." During the test of the 513GB version, it showed 1.22W at idle. Reply
  • Kristian Vättö - Wednesday, May 8, 2013 - link

    The 128GB SSD 830 idles at 0.38W (I think the firmware is also newer, the 512GB had pre-production FW as far as I know). As always, you can find all our SSDs (and other components) in the Bench, here's the 128GB SSD 830:

    http://www.anandtech.com/bench/Product/533
    Reply
  • cactusdog - Tuesday, May 7, 2013 - link

    I don't understand why Seagate and WD were so slow in the SSD market. They should have a complete range of SSDs by now. They could have just rebranded OEM drives (if they didn't want to spend money) and would have sold millions just from their name alone. Like Kingston and others did...... I don't get it. Reply
  • Sabresiberian - Tuesday, May 7, 2013 - link

    I wonder if the main HD manufacturers here were doing a bit of "American auto industry" thinking. Like "We sold all the gas guzzlers we could make before, how are we supposed to know the general population is going to want cars that get better gas mileage?" Chrysler and GM had to be bailed out twice for that kind of thinking.

    So, were Seagate and Western Digital thinking "We're selling all the HDs we can make, why should we get into SSDs?" I don't know, but it's an explanation that seems to fit, to my way of thinking anyway.
    Reply
  • Powerlurker - Tuesday, May 7, 2013 - link

    I think it's more that Seagate and WD have extensive expertise in manufacturing HDDs that can't be replicated by competitors and lots of industrial infrastructure that only they (and Toshiba at this point) have. Meanwhile, on the SSD front, they would be competing with any idiot on the Pacific Rim with a reference design and a pick-and-place line. SSDs are rapidly becoming commodity products at the consumer level and long term profitability in the segment requires you to have your own special sauce (controller technology, firmware expertise, a NAND fab, or some other unique advantage) which WD and Seagate don't really have at this point. Reply
  • Kristian Vättö - Tuesday, May 7, 2013 - link

    While WD and Seagate lack the SSD expertise, they have the distribution channels and resources. Hynix is a good example of a company that has all the expertise they need to develop a competitive SSD but their distribution channel is lacking. Seagate, on the other hand, operates globally and can reach billions of potential buyers in a short period of time. Even if you have a good product, it's fairly meaningless if it can't reach most of the market. Hynix actually makes SSDs but they are doing absolutely nothing to market them and I bet they don't have many distributors in the US or other Western countries (NewEgg sells their SSDs but I haven't seen them elsewhere).

    Seagate also has tons of capital to invest on the SSD market. Like in the case of this SSD, they didn't just go with stock SandForce but chose LAMD and invested on specializing the firmware. On top of that, I'm pretty sure Seagate has fairly big NAND deals with Toshiba and Samsung to ensure a steady supply of NAND, which requires capital. There have already been NAND shortages in the market and this year it will get even tougher - Seagate has an advantage because they can buy a ton of NAND whereas smaller players lack the capital for that (and the bigger client you are, the more important you are for the company so big clients are prioritized when there's a shortage).

    What would be a killer combination in the future is Seagate and Hynix combining their powers.
    Reply
  • secretAgent! - Tuesday, May 7, 2013 - link

    WD is coming out soon with SSD PCIe cards soon.... i've helped test them.... shhhh.... Reply

Log in

Don't have an account? Sign up now