Someone recently asked The SSD Guy if there is a way to determine whether an SSD is SLC, MLC, eMLC or TLC.
I found it a little odd to be asked this, since most vendors tell what kind of flash they use in an SSD’s specifications, especially if it’s SLC.
Not finding it there then the next thing I would look at is the price. Raw SLC NAND flash now sells for about 6-10 times as much as its MLC counterpart, so an SSD with a price of around $1/GB is likely to be MLC and one that sells for around $10/GB is probably SLC.
TLC SSDs are really rare. There is the 840 from Samsung and the Ultra II and X300 from SanDisk. It’s also pretty rare to find an SSD that is based on eMLC, because eMLC achieves its higher endurance by slowing the part down. There are other, better ways to extend endurance.
Now that you know all this, please note that the kind of flash used to produce the SSD is probably unimportant. Certain MLC SSDs outperform some SLC SSDs, both in speed and in endurance – it all has to do with the quality of the controller. There’s a thorough explanation of this in The SSD Guy’s series on SSD controllers.
Furthermore, NAND chips allow controllers to change flash pages inside the chip from TLC to MLC to SLC as needed, so some SSDs actually internally manage hot data to SLC and cooler data to MLC or TLC.
For those that have read this far, I would recommend changing your focus away from questions of SLC vs. MLC vs. TLC and focus instead upon the SSD’s published specifications (like speed and endurance) and on its SMART attributes. The SMART attributes will always tell you how your SSD is wearing, and the specifications will tell you how it is expected to perform.
If you don’t trust the manufacturer’s performance specifications, then I highly recommend using the SNIA performance test specification, which gives unbiased performance results for any SSD.
Samsung recently introduced its 3D V-NAND-based 850 SSD which, according to The Tech Report, uses the same MEX controller as the company’s 3-bit planar SSD, the 840, introduced last year.
Samsung said in its keynote speech at the 2013 Flash Memory Summit that V-NAND consumes an average of 27% less power and runs at least 20% faster than its planar counterpart in an SSD application, all while providing ten times the endurance. It’s only natural to assume that this would allow designers to produce a V-NAND SSD that would significantly outperform its planar NAND counterpart.
In his Flash Memory Summit keynote on Wednesday, Micron VP and Chief Memory Systems Architect Ed Doller made a compelling demonstration of the power and performance advantages of a new approach to computing.
With true showmanship, Doller had his co-workers hand out buttons with LED lights to the entire audience. The LEDs in these buttons were either green or blue, with the colors randomly dispersed among the crowd. Doller asked the entire audience to turn on their lights, then called one row of the audience to file up to the stage so he could determine whether each person’s button was blue or green.
He pointed out that this was like having a single CPU check the contents of a drive. He then asked why things should work this way – wouldn’t it be more sensible to Continue reading
At last week’s International Solid State Circuits Conference (ISSCC) Shuhei Tanakamaru, a researcher from Japan’s Chuo University, detailed a scheme to reduce MLC SSD bit error rates (BER) by 32 times over conventional techniques. The approach used an impressive combination of mirroring, vertical and horizontal error correction, and a deep understanding of the most likely kinds of bit errors flash will experience.
This is a very novel and well-conceived technique that may find industry adoption in future SSDs.
The steps included in the paper are used in addition to the Continue reading
SNIA (The Storage Networking Industry Association) has conferred a great honor upon the SSD Guy by bringing all of the blog posts in the series How Controllers Maximize SSD Life into a single printed volume of the same name.
Readers can either ask for a print copy from SNIA, or can download a pdf rendition by visiting the SNIA SSSI (Solid State Storage Initiative) education web page.
During this month’s Storage Visions conference, SMART Storage Systems hosted a “NAND Band” party. The company kept the details secret until the guests were all there, after which two “Blues Brothers” impersonators (SMART’s president John Scaramuzzo and Rick Neff, Director of Business Development) showed up in a video singing their new rendition of the 1966 Spencer Davis Group hit: “Gimme Some Lovin’.” SMART’s version was called: “Gimme Some Endurance” and the lyrics centered around the importance of endurance in SSDs.
(SMART’s NAND Band should not be confused with the techno band named NAND which I only discovered while writing this post.)
The reception was held only a couple of hours after Continue reading
This is a bad day for The SSD Guy. I just finished publishing an eight-part series explaining How Controllers Maximize SSD Life, then my evil twin The Memory Guy today published a post telling of a new flash design from Macronix that might just eliminate the flash wear-out mechanism!
But my concerns are inconsequential compared to the feelings of all those folks who have devoted phenomenal time and energy to develop wear management algorithms.
Given that you have used all those other forms of improving SSD wear that we have discussed so far, but you still don’t find that this is enough, what do you do next? Well a few SSD controllers go one step further and manage some of the inner workings of the NAND flash chip itself.
If that sounds like a significant undertaking to you, then you clearly understand why so very few controllers take this approach. The information used to perform this function is not generally available – it takes a special relationship with the NAND flash supplier – and you can’t develop this relationship unless the NAND supplier Continue reading
One way that SSD controllers maximize the life of an SSD is to use feedback on the life of flash blocks to determine how wear has impacted them. Although this used to be very uncommon, it is now being incorporated into a number of controllers.
Here’s what this is all about: Everybody knows that endurance specifications tell how much life there is in a block, right? For SLC it is typically 100,000 erase/write cycles, and for MLC it can be as high as 10,000 cycles (for older processes) but goes down to 5,000 or even 3,000 for newer processes. TLC endurance can be in the hundreds of cycles. Now the question is: “What happens after that?”
In most cases individual bits start to Continue reading