Performance Consistency

Performance consistency tells us a lot about the architecture of these SSDs and how they handle internal defragmentation. The reason we do not 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 or cleanup routines directly impacts the user experience as inconsistent performance results in application slowdowns.

To test IO consistency, we fill a secure erased SSD with sequential data to ensure that all user accessible LBAs have data associated with them. Next we kick off a 4KB random write workload across all LBAs at a queue depth of 32 using incompressible data. The test is run for just over half an hour and we record instantaneous IOPS every second.

We are also testing drives with added over-provisioning by limiting the LBA range. This gives us a look into the drive’s behavior with varying levels of empty space, which is frankly a more realistic approach for client workloads.

Each of the three graphs has its own purpose. The first one is of the whole duration of the test in log scale. The second and third one zoom into the beginning of steady-state operation (t=1400s) but on different scales: the second one uses log scale for easy comparison whereas the third one uses linear scale for better visualization of differences between drives. Click the dropdown selections below each graph to switch the source data.

For more detailed description of the test and why performance consistency matters, read our original Intel SSD DC S3700 article.

SanDisk Ultra II 240GB
25% Over-Provisioning

The IO consistency of the Ultra II is not too good. At steady-state it averages about 2,500 IOPS, whereas MX100 and 840 EVO manage around 4,000-5,000. However, what is positive is the fact that it takes about 200 seconds before the performance starts to drop, which is mostly due to the fact that the Ultra II does not provide as many IOPS in the first place.

Since we are dealing with a value client drive, I would not consider the IO consistency to be a big issue because it is very unlikely that the drive will be used in a workload that is even remotely comparable to our performance consistency benchmark, but nevertheless it is always interesting to dive into the architecture of the drive. While the Ultra II is not the fastest SSD, it is still relatively consistent, which is ultimately the key to a smooth user experience.

SanDisk Ultra II 240GB
25% Over-Provisioning


SanDisk Ultra II 240GB
25% Over-Provisioning


TRIM Validation

To test TRIM, I filled the Ultra II with sequential 128KB data and proceeded with a 30-minute random 4KB write (QD32) workload to put the drive into steady-state. After that I TRIM'ed the drive by issuing a quick format in Windows and ran HD Tach to produce the graph below.

And TRIM works as it should.

The Introduction, The Drive & The Test AnandTech Storage Bench 2013


View All Comments

  • hojnikb - Thursday, September 18, 2014 - link

    Some people with 840 basic are also reporting slow read.. Reply
  • CrazyElf - Tuesday, September 16, 2014 - link

    Factoring in the power loss protection and the fact that you get MLC, albeit at 16nm, I'd say that the MX100 represents a superior drive to this SSD. Oh, and the Ultra II does not support encryption.

    Arguably none of these shortcomings would be a problem for a consumer based drive for the average user, but this drive brings no real advantages over the MX100 in terms of pricing, performance, etc, and several drawbacks.
  • sweeper765 - Tuesday, September 16, 2014 - link

    I wouldn't rush into buying a TLC based drive right now, seeing the problems 840 EVO series is having.

    There are hundreds of users reporting heavy read speed degradation of old written data, reaching only 50mb/s or even 2-3 mb/s in the most extreme cases. Might be a firmware bug but also could be a TLC issue. Who knows?
  • NA1NSXR - Tuesday, September 16, 2014 - link

    So basically a wash, or even arguably a slight loss against 840 EVO, with 850 EVO on the horizon. I don't know if I would've personally given it a "Recommended by Anandtech". Reply
  • Kristian Vättö - Wednesday, September 17, 2014 - link

    The 840 EVO is more expensive and not just marginally. While the 850 EVO is coming and may very well be the best value drive when it does, at this point it is just another product in the pipeline. Making recommendations based on a future product that may or may not be faster wouldn't be far in my opinion. Reply
  • Gigaplex - Wednesday, September 17, 2014 - link

    The only reason I'd consider a TLC drive over an MLC drive is if it was significantly cheaper than competing MLC drives. It's no cheaper than MX100 at 512GB and below, and not that much cheaper than M550 at 1TB. At 50% higher bit density per cell, I was hoping for ballpark 33% cost reduction. Reply
  • hojnikb - Wednesday, September 17, 2014 - link

    Sadly, it doesn't work like that. Even though it has TLC, most consumers won't care. Sandisk obviously positioned the drive in a price bracked, similar to competition. Reply
  • rtho782 - Wednesday, September 17, 2014 - link

    In most of these reviews I see complaints about lack of encryption support.

    Why would I, as a home user, want to encrypt my drive? Does it not require additional software and/or motherboard support and mean I can't move the drive to another PC?

    I know businesses like to encrypt their laptops, but I don't understand how encryption would benefit me.
  • jabber - Wednesday, September 17, 2014 - link

    Unless you really need it for business/legal needs then encryption is a liability in terms of you screw up your drive and then you want to pull any data off it. Certainly never encrypt a drive you use for testing/tweaking/overclocking a PC with thats asking for trouble. If you have a porn collection you want to hide then simply use encrypted file containers. Much safer than full disk for the average Joe. Even those that need encryption by law often don't actually have data worth looking at but it's there to save embarrassment. In 99.9% of cases encryption is only needed to stop the guy that found or stole your laptop looking at what's on there for 2-3 mins before a dodgy copy of Windows 7 or Linux is slapped over the top and the laptop is sold on. Reply
  • Kristian Vättö - Wednesday, September 17, 2014 - link

    Our readership is much more than just home users. Many IT managers come to AnandTech to aid their hardware buying decisions, so we want to cater more than just the typical enthusiast needs. Besides, hardware encryption is still a feature after all -- whether you need is up to you like I mentioned in the review. Since some drives in the same price segment have it and others don't, I think it is something that should be noted because having it is better than not having it in any case, even if you don't use as you never know if your needs change. Reply

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