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aspects of SSD design
processors used in SSD controllers and systems
real examples from the market - (preview)

by Zsolt Kerekes, editor - StorageSearch.com - October 12, 2015

This is a heads up about an imminent future series of article on StorageSearch.com which will comment on the many different approaches which designers have used in the SSD market to choose the type and number of processors which are integrated in SSD controllers, and in solid state storage drives and systems ranging from SSDs on a chip upto rackmount arrays. The new series will include stories around subjects like:-
  • how many processors are used in a real SSD? (If the answer was that obvious - I wouln't have planned a whole article to deal with this single question.)
  • which processor architectures are in use?
    • standard?
    • stretch?
    • roll your own?
  • how have real SSD designers chosen the processors for their controller designs?

    (the almost boring realities - not the gilded fairy tales)
  • when multiple processors have been used in the same design - how have real designs varied with respect to these parameters:-
    • clones (more cores the same),
    • aliens (entirely different processors which somehow beamed their way into the design) and
    • drones (dumber than processors but smarter than slaves).
  • roadmap constraints which come from the markets and applications in which the SSDs will be deployed
    • physical space
    • budget
    • power
    • workload characteristics
    • life-cycle
    • politics
  • architecture and patent tricks inside processors
    • Things you expect like - power management, data integrity.
    • Sneaky stuff like nvm inside the controller, security features etc.
The first article in this series will appear in November 2015.

Now you may ask - who will be interested in such articles? And where will the content come from?

As to who may be interested?...

That's hard to predict. Who would have thought at the outset of these SSD articles that so many people would become so interested in a directory of companies which design SSDs?, or the impact of flash endurance on SSD design complexity?, or the nitty gritty details of classic wear leveling in SSDs?, or a list of SSD controllers?, or a guide to adaptive R/W and DSP ECC? Yet each of these subjects grew to become highly read - partly as a result of the SSD market growing - but also because enough of their readers played a part in helping the SSD market to grow.

So I've stopped being surprised by the fact that topics which once seemed arcane and only of interest to a small number of specialists - mushrooms years later into the mainstream.

As the possibilities for deploying SSDs with application specific power, performance, and storage/server/app optimimized role becomes better understood - it has now become inevitable that thousands of systems design groups are not only looking at designing their own SSDs (which has been happening for years already) but also a heck of a lot of these designers are also looking at deeply customizing the SSD in their life - with customization which aims far beyond adding a few firmware tweaks to a COTS SSD controller and choosing the flash to populate someone else's reference design.

This is partly because as tools get cheaper people aspire to do more stuff. Competitive forces kick in. Ecosystems get started.

Ask yourself this - how many people in the world in 1974 could write programs for microprocessors?

Yet somehow we got from needing to know assembly language and what the connected chips did to a world where if you can type the right stuff you're streaming a movie about social networks.

Would the quality of software be better if we could move back to a pre Microsoft era? While it's unfortunate how much time in the world gets wasted by that X per cent of bad code - the other (100 minus X) per cent is big enough to mean you can get a lot of useful things done in between updates.

It's a tough life designing new SSDs and not as glamorous as civilians might think. You spend a lot of time waiting for stuff to be ready and in meetings and email. And looking at some more web pages about processors in SSDs isn't going to make your working day shorter.

Here's my sales pitch to get you interested....

In a way - everything in electronics design is obvious - once you know it's already been done (and how) - so you might find these articles useful for a varierty of reasons because you'll think to yourself.
  • I can do better than that, or
  • I've already done better things than that, or
  • is that all there really is to it?
Which will make you feel good.

As to where will the commentary will come from?

About half the content will come from datamining conversations which I've already had with designers of new SSDs, controllers and systems. At the time those original stories were written - the story was - the SSD. Who cared about the internal processor? or how it got there? But we often discussed the processor angle too and how that impinged on the SSD design architecture and roadmap. I've still got notes and recollection from those many part conversations. And I'll also be reaching out to people I know who have interesting insights which they can bring to these future articles. And if there's not enough from those sources I'll see what I can find in other sites for you to look at. And if all else fails I'll just make stuff up.

The level of the articles?

Here's my apology in advance. Due to various form factor and packaging issues I can't change my brain too much right now. Unfortunately it's the same one I've had for as long as I can remember. Better than new in some ways - but not as good in others. Some bits have worn off and some of the upgrades which I patched in may not have been attached in the right places. Meaning that the style of the new articles will be similar to many past articles here on the mouse site.

I assume that you're an expert and probably know a lot more than me about what you do every day. So I'm not going to tell you low level idiot stuff - like what's the best way to set up your design tools to get insights from your system simulations.

That's up to you and how you share design responsibility between what goes on in your head and what goes on in software (and how you borrow resources from other projects).

What I hope to bring to these articles is this. I talk to a lot of people about the changing weather in SSD land. We still can't predict the weather accurately. And until it rains we still can't be sure if it was a good idea to plan that picnic. But we've got the food and drinks in anyway and the tables are ready and until the storm bursts over our heads and washes us all away we're going to try and enjoy what we're doing now - even while we puzzle out what all those strange colors in the SSD sky might mean.

So I hope to see you soon with some thought provoking processor design examples stories from the SSD history archive.

If you'd like to contribute your own anecdotes or insights to any of these future articles - the easiest way is to contact me by email.
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I don't think we've reached stability in reference enterprise SSD designs and use cases.
what kind of SSD world did we expect?




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How many processor cores in the SSD controller?

2013 - 3rd generation SandForce SSD controller family - the SF3700 - had 14 cores

2015 - Mangstor's PCIe SSD - MX6300 - has 100 cores




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With thousands of projects now designing new SSDs - and so many untapped application roles there just won't be enough standard SSD controller types around to do what needs to be done.




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"To further increase performance, controllers can take advantage of interleaving. Each NAND flash chip can have multiple dies in it, this is particularly so for high density parts. 2/4/8 die packs are common."
Nand channels and banks - an SSD controller primer




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Compared to earlier phases in the SSD market more is changing.

memories (We used to be able to write down a list of those which mattered. Now we're seeing many new strangers from strange lands. Even I can't remember who they all are and how to spell their names.)

controllers (Let's not even get started on this subject.)

firmware (Shouldn't this be grouped with controllers? If only it were that simple.)
the SSD Bookmarks - here we go again