Know Your SSDs - SLC vs. MLC

Memoright 128Gb SSD Review – Part 2 or

Know Your SSDs - SLC vs. MLC​

By Les Tokar

Introduction

This article is written to follow in the footsteps of an excellent review by Kevin O’Brien on the Memoright 128Gb solid state drive (SSD). His article provided many great benchmarks, to include HDTune, HDTach and ATTO Disk Benchmarking, which have gained a reputation of accuracy and reliability over the past few years. It’s refreshing to see a secondary reviewer who can validate claims of the capabilities of SSD’s along with offering his own opinions, a positive characteristic we see in all reviews here at NBR.

​

In this article, we are going to build on the first by showing why the Memoright 128Gb SSD is so unique and will mostly likely hold a very solid footing in SSD sales for a long time to come. We will do this by explaining a bit of the inner componentry of the SSD, performance considerations, why they are priced as they are along with how this will soon change creating a flurry of sales in the consumer SSD market within the next year.

This article is a MUST READ for anyone contemplating buying a SSD in the near future and will most likely hook many who are walking that line in the sand.

As a bonus, we are going to reveal information that is presently a very sensitive spot with many manufacturers. This information pertains to the surprising lifespan of soon to be manufactured SSDs that you will need to know and understand.

Every Little Bit Counts

The SSD, at its most basic level, is comprised of bits, lots and lots of bits. To try and build from the bit and explain how we reach a total of 128Gb SSD would scare most off. Understanding the bit, however, will bring us to an understanding of two different types of SSDs, the slc (single level cell), or the mlc (multi level cell) design. Our understanding of these two is crucial to our SSD purchase.

An slc SSD, such as the Memoright 128 GB SSD, is simply built where 1 bit rests within 1 cell of the SSD. Conversely, a mlc SSD means there are two bits within 1 cell of the SSD. The best way of understanding this is to compare a cell with a single bit to a single home whereas a cell with two bits would be a duplex. For those capable of using the slc SSD to its full potential, it is easily understood that they have much more control over the total SSD as each bit is within it’s own cell. Its much the same as trying to make alterations on your single family home, vice a duplex.

Where we need to pay attention, however, is with failure of the SSD as it occurs at the cell level. In a duplex, both sides are lost by fire vice only the one with a regular home. This is much the same as losing both bits in a mlc, vice the single bit of the slc. This directly affects the lifespan of the mlc compared to the slc which will be covered ‘in just a bit’.

Suffice it to say, we can form a basic understanding that the slc SSD, as with the Memoright 128Gb design, is much better than the mlc SSD.

How Fast is Fast?

Presently, the only SSD capable of reaching performance results in excess of 100MB/s read and write at the 128Gb capacity is the Memoright 128Gb SSD. This may remain as such because many consumer manufacturers seem to be experiencing a problem simply fitting 128Gb NAND into a 2.5” SATA SSD. Having spoken to several, they seem to agree on the simple fact that, in no time soon, can the slc design reach the average consumer at 128Gb or above, for the most part because it cannot be made at a cost effective price.

As a result, manufacturers are furiously testing and manufacturing mlc SSDs for consumer sales because they can reach higher capacities at a cost within the consumers reach. There are performance hits though. Most manufacturers admit that mlc SSDs will rest in the area estimated at a maximum of around 90MB/s read and 50MB/s write, this well below the slc design. Could this be good news for the Raptor? Read on!

The Performance Misconception

The true performance of an SSD cannot be understood unless one has had the opportunity to utilize one. Even watching a short demo is not a fair representation. We are so used to grading the performance of a HD by its read and write benchmarks that we instinctively look to this from the SSD as well.

The magic of the SSD comes less so from the read and write benchmarks and more so from the incredible access speed that it can achieve. An SSD searches similarly to that of your computer. It finds something by index and then retrieves it from NAND as the computer would from RAM.

There are no moving parts involved and this occurs as quickly as 0.1ms.

With the typical consumer owned hard drive, it takes 10-15ms, on average, to find information and retrieve it because of the disk spinning, arm pivoting above and having to find the information on each pass and so on. This is compounded by the fact that a large file on a HD can take several passes to retrieve, each pass being 10-15ms on average compared to the 0.1ms total time of the SSD. This is why so many programs seem to open instantly with an SSD vice the HD. This is the true guts of the SSD.

​

How Long Will They Last

I am very close with many SSD manufacturers of both the enterprise and consumer arena. I have asked this question of many and must admit that the most frank response is “MLC lifespan is a little sensitive with manufacturers. Each is trying to cope with this answer very carefully.” The true answer to the question for both slc and mlc SSDs is this…

“The SSD will outlive the hardware for which it was built for.”

SLC ssds can be calculated, for the most part, to live anywhere between 49 years and 149 years, on average, by the best estimates. The Memoright testing can validate the 128Gb SSD having a write endurance lifespan in excess of 200 years with an average write of 100Gb per day.

This is where the mlc design falls short. None have been released as of yet. Nobody has really examined what kind of life expectancy is assured with the mlc except that, it will be considerably lower. I have received several different beliefs which average out to a 10 to 1 lifespan in favour of the slc design. A conservative guess is that most lifespan estimates will come between 7 and 10 years, depending on the advancement of ‘wear leveling algorythms ’ within the controllers of each manufacturer.

To draw comparison by way of write cycles, a slc would have a lifetime of 100,000 complete write cycles in comparison to the mlc which has a lifetime of 10,000 write cycles. This could increase significantly depending on the design of ‘wear leveling’ utilized.

Understanding Pricing

DVNation sells the Memoright 128Gb SSD for $3399. There is a lot of reasoning behind this, the first of which is the price of NAND. It presently floats around $11/Gb on an 8Gb chip (slc) which has dropped some 60-70 percent in the last year. To understand why mlc ssds are going to arrive much cheaper, we need to understand that mlc NAND sells for considerably less, at roughly $3.50 per Gb at the time of this writing some 63% cheaper. You can watch the price of NAND here at the bottom table entitled ‘Flash Contract Price’. The NAND which we are looking at is 8Gb 1024Mx8 (slc or mlc) and the price point reflects cost per gigabyte. Below, we can get an idea of the dropping price of NAND over the last two years.

​

From here we also need to look at manufacturer controllers which may differentiate a great deal from manufacturer to manufacturer. Add on the casing, profit by manufacturer and then the profit by reseller and we may understand why slc design will remain as the premium SSD for those that can afford it.

Conclusion

Through a very conservative general estimate, the sale of SSDs will go through the roof within the next few months, most resulting from the fury of mlc ssds which will hit the market any time now at a price well below half of the slc ssd. We can now see that, as with auto manufacturers, you will have the option of purchasing the Cadillac or the GM of the SSD.

As costly as it is, the Memoright 128Gb SSD is now and will remain the ultimate SSD to own, not only because it is the only 128Gb slc design SSD available to the consumer, but because it will outlive and outperform any other consumer SSD on the market. Somehow, Memoright has found a way to push in the capacity that many seek as well as finding the performance that many will pay the premium for.

We are now fully prepared for the onset of the SSD revolution as one can, not only differentiate between a slc and mlc SSD but also, understand the pricing, performance and lifespan considerations of each.

 

Awesome Flamenko! What is the price?

 

The price of that drive is...stated and steep but that of the mlc drives will be much cheaper. I expect to be delivering news anytime on he first mlc releases, however, companies won't release final pricing as of yet. I can say they will be in reach of many of us though.

 

To be honest with you; at this point in time the jury is still out on the lifespan of the Memoright drive.

I'd actually prefer a Median value rather than a mean/average value; although in fairness in a prototypical Gaussian distribution the mean and medians tend to converge.

I'm also somewhat skeptical of the techniques used to calculate the way high MTBFs that we see. How do you get to a 1 Million Hours MTBF? Run 1000 drives for 1000 hours, with one failure that's 1 Million MTBF. If one looks at the probablity of a single device to last to the MTBF; that's an entirely different prospect... It's < 50% for any given device.

I'm not saying this to slam the claims; but rather to offer a small dose of salt and reality...

 

Once again, an excellent guide/review. I didn't know there was a difference in SSDs (slc vs. mlc) until now. Very informative. I just hope SSD prices go down in a few years because I really want one!

 

Very good post. Some day all will recognize wear is not the big issue people want to make it out to be. But until then thank you for trying to explain. 7 years is enough if you know. Some people love being "Devil's Advocate" and pretending they are using 7 Year old computers and loving it? Not! So what issue?

 

Great article flamenko, makes it much easier to understand the differences between MLC and SLC SSD's.

I just wish that they would make it to shelves quickly to drive prices downward. I have no problem with getting a MLC drive, and the current memory prices make it seem that they will be affordable in the not too distant future.

A 7 year lifetime is really no problem for most people, since in 7 years it is entirely likely that we won't be counting in GB's anymore, having moved to TB's and PB's. 7 years of physical lifetime will outlast the practicality of the drive. I don't see any reason for an individual to buy a SSD to last 100 years, since they will probably stop using it in 3-5.

Greg

 

Agreed.

I'd be perfectly happy with an MLC SSD. 7-10 years is fine. I've had my HDD for almost two years now and I'm already looking for another notebook(with new HDD or SSD).

MLC SSDs are still better then traditional HDDs.

Fantastic article flamenko! As always.

 

Right now the industry seems to be in a period of rush rush to get the first mlc drives out. Mtron expected to have them out by Feb 12 but ran into a delay and now expects the beginning of March. Pricing is a hard answer to get from any company because their recommended retail price and end selling price has been drastically different thusfar. Lets face it, SSDs for the most part have been reserved for those that can afford it in the last few months unless, like me, you were able to negotiate a great price from Dell.

This will change soon enough and I know this because companies seem to be contacting me suddenly and all are reflecting roughly the same time period, those to include Mtron, Crucial, Memoright, Ridata as well as Samsung.

I have people trying to get me a Samsung SATA II straight from the factory in the first shipment out. Their initial SATA II will be a great OEM inclusion as they state their will be little if no price increase yet, their appears a 100% performance boost.

From there, they will be introducing a mlc 250Gb ssd by years end as detailed here.

Prior to this, I believe companies were at that stage where they were asking themselves how many would they want to manufacture with the price being out of the consumers reach, strictly because they were costing that much to make.

I think it will be an exciting few months and hope to have some especially good news soon.

 

not sure if this is new information or not, but...

From my company's Dell rep: