Silicon Motion SM2256 SSD Controller Preview: TLC for Everyone
by Kristian Vättö on June 17, 2015 8:15 AM EST- Posted in
- Storage
- SSDs
- TLC
- Silicon Motion
- SM2256
Final Words
To get the elephant in the room out first, I'm not overly satisfied with the performance. The SM2256 is slower than the other TLC SSDs (850 EVO & Ultra II) on the market and not just by an insignificant margin. Especially small size random IOs are rather slow, which impact the overall performance because many IOs in client workloads are 4KB and random in nature. For very light IO workloads that obviously won't be a major issue, but anything more IO intensive (like virtualization) could be severely impacted by SM2256's high latency. To be frank, I never expected the SM2256 to perform like the SM2246EN because no controller can get around the performance limitations of TLC NAND, but given how well the SM2246EN performs I was expecting the SM2256 to be faster than it is.
Aside from performance, the other problem with SM2256 is its power consumption. The part I absolutely love in the SM2246EN is its extremely low power consumption, but the SM2256 practically doubles the power draw that makes it one of the least efficient drives we have tested. Again, expecting the SM2256 to be as efficient as the SM2246EN wouldn't be fair because TLC inherently has higher power consumption as it needs a higher number of program-verify iterations, but even then doubled power consumption is a bit more than I was looking forward to.
I do wonder how big of a difference the NAND makes, though. As I mentioned on page one, we will likely never see this configuration on the retail market because Samsung doesn't sell its TLC to third parties in large quantities, so I'm not sure if Silicon Motion has spent a ton of resources in optimizing the firmware for NAND that won't be used outside of engineering samples. I certainly hope that the SM2256 performs better with NAND from other vendors because as it stands the performance is quite underwhelming against the competition, but nothing that couldn't be fixed with better optimization. After all, the sample I have doesn't have the final retail firmware in it, so we will have to wait for shipping drives before drawing the final verdict on the SM2256.
In any case, it will all boil down to pricing anyway. If Silicon Motion's OEM partners can drive the prices down with the SM2256, I will be totally fine with the performance because the SM2256 is still more than fine for basic usage. TLC SSD pricing was actually one of the things I was very vocal about at Computex because OEMs can't price their TLC drives similarly to the MLC ones and expect it to be a good sale. TLC isn't as good as MLC and that's a fact that nobody can deny. Especially after Samsung's issues with TLC the market has become more skeptical about TLC in general, so saving a few bucks isn't enough anymore for the educated buyers to choose TLC over MLC -- I think the difference has to be in the order of 10% or so to be worth the lower performance and possible long-term reliability risks that TLC brings. I do believe that the SM2256 is a vehicle capable of delivering such cost savings, but for now we will just need to wait and see what happens.
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Death666Angel - Wednesday, June 17, 2015 - link
"I just can't recall a review of a flagship device that wasn't out within 2 weeks of release"Weren't most Note phones, HTC Nexus 9 and Nexus 6 pretty late or only in preview format released? Anandtech is notorious for this stuff when it comes to anything but Apple. :D Though more often than not, eventually we get something.
Michael Bay - Thursday, June 18, 2015 - link
Just two weeks?I`m still waiting for 960 review.
Oxford Guy - Thursday, June 18, 2015 - link
"TLC for everyone?" Maybe if the drives are being given away. The last time I checked MLC isn't that expensive.Oxford Guy - Thursday, June 18, 2015 - link
Samsung has had "some issues" with TLC, eh? Why not specifically state what those are?"Like all TLC SSD designs we have seen, Silicon Motion employs SLC caching in the SM2256 to improve performance and endurance. The size of the SLC cache is configurable by the OEM, but generally the cache size is between 3GB and 12GB depending on the capacity of the drive."
Actual SLC or some sort of simulated SLC?
canthearu - Thursday, June 18, 2015 - link
"Actual SLC or some sort of simulated SLC?"Both the same really. As long as it is dedicated space that will never be asked to perform TLC duty.
Oxford Guy - Saturday, June 20, 2015 - link
Isn't it rather impossible for triple layer NAND to be single layer NAND?DeepStorage - Sunday, June 21, 2015 - link
Most flash foundries have at least some models of their MLC, and TLC flash that can dedicate some percentage of the pages per die to use in SLC mode. It doesn't have quite the performance or endurance of pure SLC but it's close.Oxford Guy - Wednesday, July 15, 2015 - link
" It doesn't have quite the performance or endurance of pure SLC but it's close."Any data on that to link to?
Kristian Vättö - Thursday, June 18, 2015 - link
"TLC for everyone" meaning that now every OEM can build a TLC drive if they wish.SLC cache implementation depends on the NAND. NAND vendors do have special dies with SLC cache functionality (supports a special command set), but so far they haven't sold them to third parties, although I've heard this is about to change. In other cases SLC cache simply means that the controller only writes to the lower pages, which in terms of write performance is about the same as real SLC cache but there is some minor read performance penalty (although I don't know exactly why).
dcaxax - Thursday, June 18, 2015 - link
"admittedly Samsung has had some issues with TLC"That's the understatement of the Millenium. My 840 and 840 Evo have such severe performance degradation (60-70%) that their speed is now visibly impaired and actually compares with some of the fastest HDDs.
Considering the price per GB of an SSD that is completely unacceptable and constitutes a ripoff.
Vendors like Samsung are fobbing off substandard parts supported by immature and unreliable technology to unsuspecting customers.
This is the equivalent of a car with flashy design and big engine which is guaranteed to develop problems as soon as you drive 100 miles. They have a name for it and it's called 'a lemon'.