MLC – The SSD Guy Blog

The Micron QLC SSD – No Surprises Here

Last Monday, May 21, Micron introduced the industry’s first QLC SSD for enterprise applications. Micron’s press release is HERE.

Although this is a laudatory feat, the industry has been headed in this direction for a number of years. In fact, this was the subject of a presentation that I made to the Storage Networking Industry Association (SNIA) during its Winter Symposium in January 2014.

The slide in which I discussed this appears as this post’s graphic. (Click on it to see a larger rendition.) This table attempted to illustrate that all SSDs were headed towards TLC (and implicitly QLC) over the long term despite the fact that naysayers persistently argued that this could never happen. It looks at attitudes over history and considers the fact that things that the industry said could “Never” happen ended up eventually becoming the mainstream technology.

Since I live, eat, and breathe Continue reading “The Micron QLC SSD – No Surprises Here”

WDC: No SSD/HDD Crossover

Those who have been reading posts on The SSD Guy blog for some time have often heard me explain that SSD prices will not fall below HDD prices anytime soon. Last week Western Digital shared a roadmap that shows that we can expect for there to be a sizeable price gap between the two technologies at least through 2028.

Let me stop for a moment to point out that Western Digital Corp, or WDC, no longer has any reason to take sides in the HDD vs. SSD battle now that the company has acquired SanDisk, a leading SSD maker. Even before that, WDC’s HGST business has been the market leader in SAS SSDs for a number of years. WDC doesn’t take sides in arguments about SSDs vs. HDDs. Instead the company stands ready to sell whichever one the customer finally decides to use.

This post’s graphic comes from a chart that WDC used on October 11 when introducing its new MAMR head technology, which the company expects to propel HDD capacities up, and HDD price per terabyte down, for a number of years. To create this chart WDC’s HDD team joined forces with the SanDisk flash team to project both HDD and NAND price per terabyte for the next 11 years. The most important conclusion is that Continue reading “WDC: No SSD/HDD Crossover”

MLC vs. eMLC – What’s the Difference?

From time to time IT managers ask The SSD Guy if there’s an easy way to compare SSDs made with MLC flash against those made using eMLC flash. Most folks understand that eMLC flash is a less costly alternative to SLC flash, both of which provide longer wear than standard MLC flash, but not everyone realizes that eMLC’s superior endurance comes at the cost of slower write speed. By writing to the flash more gently the technology can be made to last considerably longer.

So how do you compare the two? OCZ introduced MLC and eMLC versions of the same SSD this week, and this provides a beautiful opportunity to explore the difference.

As you would expect, the read parameters are all identical. This stands to reason, since Continue reading “MLC vs. eMLC – What’s the Difference?”

What’s In My SSD? SLC, MLC, or TLC?

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 Continue reading “What’s In My SSD? SLC, MLC, or TLC?”

Kaminario Goes All-Flash

Kaminario has introduced the 4th generation of its K2 enterprise-grade storage array. Unlike the company’s earlier K2s, which supported DRAM, SSD, and HDD, the fourth generation K2 is all-flash, based on SAS SSDs alone. The company says that its new approach reduces the cost of ownership by supporting a larger capacity within a smaller footprint while requiring less power and cooling.

The SSDs are MLC products, rather than the SLC ones used in earlier K2s, allowing Kaminario to reduce the cost. Although the SSDs Kaminario uses come with a 5-year warranty, the K2’s SPEAR operating system optimizes flash endurance allowing Kaminario to offer a 7-year warranty. (SPEAR is Kaminario’s scale-out performance storage architecture operating system software.)

The original K2 was built with a focus on Continue reading “Kaminario Goes All-Flash”

Extreme SSD Error Correction

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 “Extreme SSD Error Correction”

How Controllers Maximize SSD Life – Internal NAND Management

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 “How Controllers Maximize SSD Life – Internal NAND Management”

How Controllers Maximize SSD Life – Feedback on Block Wear

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 “How Controllers Maximize SSD Life – Feedback on Block Wear”

How Controllers Maximize SSD Life – Reduced Write Amplification

Write amplification plays a critical role in maximizing an SSD’s usable life. The lower the write amplification, the longer the SSD will last. SSD architects pay special attention to this aspect of controller design.

Unlike the other factors described in this series this is not a technique that extends flash life beyond the 10,000 erase/write cycles that one would normally expect to result in a failure, but it is very important to SSD longevity.

Write Amplification is sufficiently complex that I won’t try to define it in this post, but Continue reading “How Controllers Maximize SSD Life – Reduced Write Amplification”

How Controllers Maximize SSD Life – Other Error Management

There are more advanced means than simple error correction to help remove bit errors in NAND flash and those will be the subject of this post. The general term for this approach is “DSP” although it seems to have very little to do with the kind of DSP algorithm used to perform filtering or build modem chips.

While ECC corrects errors without knowing how they got there, DSP helps to correct any of the more predictable errors that are caused by internal error mechanisms that are inherent to the design of the chip. A prime example of such an error would be adjacent cell disturb.

Here’s a brief explanation of Continue reading “How Controllers Maximize SSD Life – Other Error Management”