Understanding Flash: The Fall and Rise of Flash Memory

This month sees the four year anniversary of some interesting events. Commonwealth countries around the world celebrated the Diamond Jubilee of Queen Elizabeth II. Whitney Houston was tragically found dead in a Beverly Hills hotel. The Caribbean was hit hard by sargassum seaweed invasion. And I made the decision to leave the comfort of Oracle databases and join the exciting new All-Flash Array industry.

Ok, I might have been stretching the use of the word “interesting” there. But for those with an interest in flash memory, February 2012 was still a very important month due to the publication of a research paper co-authored by the University of California’s Department of Computer Science and Engineering and Microsoft Research.

The paper was entitled The Bleak Future of NAND Flash Memory – and it wasn’t pleasant reading for somebody who had just abandoned a career in databases to bet everything on flash.

The Death of Flash Memory

I have never spoken to the authors of this paper so I don’t know where the “Bleak Future” title came from, but it seems reasonable to say that it was somewhat more inflammatory than the content. In the body of the paper, the authors examined the behaviour of NAND flash memory chips as the lithography shrank – and also as the number of bits per cell increased from SLC through MLC to TLC. At the time of publication the authors were examining 25nm technology but it was already obvious that this form of NAND (known as 2D planar NAND) was going to hit physical limitations beyond which it could no longer shrink. This is known in the semiconductor world as the scaling limit.

The paper concluded:

“SSDs will continue to improve by some metrics (notably density and cost per bit), but everything else about them is poised to get worse. This makes the future of SSDs cloudy”

This sentiment, along with the “bleak future” thing, caused a bit of a stir in the tech world. TheRegister, for example, ran a typically tongue-in-cheek headline: “Flash DOOMED to drive itself off a cliff – boffins“. Various industry bloggers discussed the potential of technologies like ReRAM to take over for the next decade, while HP made it’s annual claim that Memristor technology (a form of ReRAM) would soon be here to save the day. I started wondering if I should register the domain name ReRamDBA.com…

The Resurrection – Now Showing in 3D

Four years later, ReRAM is still just around the corner but now in the form of Intel and Micron’s 3D XPoint technology, while HP has significantly backtracked on its Memristor programme. Flash memory, meanwhile, is still going strong thanks to the introduction of vertical or 3D NAND.

“Reports of my death have been greatly exaggerated” – Mark Twain

Of course, hindsight is a wonderful thing. It’s easy to look back now at the publication of the Bleak Future… paper and consider it flawed. To see the flaws at the time of publication would have required a bit more thought.

So that’s why this month’s hero is Allyn Malventano, Storage Editor for PC Perspective, who published an article on 21st February 2012 (the same month!) called NAND Flash Memory – A Future Not So Bleak After All in which he described the original publication as “bad science”. Allyn’s conclusion was so prescient that I’m going to quote it right here (although you should read the whole article to get the full context):

“The point I want all of you to take home here is that just as with the CPU, RAM, or any other industry involving wafers and dies, the manufacturers will adapt and overcome to the hurdles they meet. There is always another way, and when the need arises, manufacturers will figure it out.”

Bravo. Samsung is now manufacturing its third generation V-NAND chips, while the Toshiba/SanDisk and Intel/Micro partnerships are both going 3D. Samsung’s V-NAND has already moved from 24 through 32 to 48 layers, while it has been theorised that there is no natural limit on the number of layers possible.

Of course, there’s always the spectre of a new technology sweeping everything before it – and the big story right now is Intel/Micron’s 3D XPoint technology. Will it take over from flash in the future? Who knows.

One thing I do know is that new technologies find their rightful place when they are both technically capable and economically viable. If 3D XPoint or any other non-volatile memory product can win the day, it will leave us all better off – and hopefully without the need for alarmist research papers.

Now, if you’ll excuse me, I’m off to check on the availability of the 3D-XPointDBA.com domain name…

(You can read more about 3D NAND here)