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the Flash SSD Performance Roadmap

Predicting and Reporting Key Trends in Flash SSD Performance - upto 2012

I've often asked where I think the flash SSD market is heading in terms of performance.

Although my earlier article RAM SSDs versus Flash SSDs - which is Best? looked at the state of the art (in 2007) it didn't include a performance roadmap.

This article does. And it has a bunch of simple to remember predictions or "laws". For convenience you can think of them as "Zsolt's Laws". Or maybe "Z's Laws" is easier to spell. The first law is the only one you need to remember.

Overall this article tells you the market model assumptions I would work to if I were setting up a new SSD company to design the fastest flash SSDs.

Obviously I'm not doing that - because otherwise the many people I talk to in SSD companies around the world wouldn't be talking to me.

I've got a good crystal ball and the lucky thing about my many past predictions related to the storage market - is that if they weren't going to be true at first - then suggesting to companies that they ought to spend more time looking at things in a particular kind of way becomes a self fulfilling prophecy. My safety net is that as many designers in the industry also read these articles - if I say something that's too outrageously wrong - they correct me - before I look too ridiculous. A quick delete, cut and paste, and it's even more accurate than it was before.

The rate of speedup predicted is much faster than would be predicted by Moore's Laws - and that's the significant point. Some explanations why - are included at the foot of the article.

• Prediction 1 - Flash SSD throughput and IOPs (in traditional HDD form factors) will more than double every year in the period from 2007 to 2012.
  
  This predicts (in effect) that in 2011 a single 3.5" form factor flash SSD will be able to deliver similar throughput to some of the fastest RAM SSDs available in 2007, with over 2,000MB/s sustainable reads and writes.

• Prediction 2 - Rackmount flash SSD throughput and IOPS performance will be a multiple of the performance for a single disk. These factors have already been shown to be scalable in SSD RAID arrays.
  
  This needs little explanation as some of the results are intuitive and we've already published plenty of articles on this subject. However, some of the architectural features which are now used in SSD RAID systems - such as MFT technology - can also be designed into individual SSD disk modules.

• Prediction 3 - The asymmetry of sustained read to write IOPs will improve from 10 to 1 (the fastest devices available in 2007) - but will never achieve parity (1 to 1).
  
  As this change occurs in the market flash SSD arrays will become viable choices in many enterprise server speedup applications which hitherto had been the exclusive domain of RAM SSDs.
  
  In (typical) database applications with Read:Write ratios of 4:1, an ideal flash SSD with 10:1 R/W IOPS is approximately 3x (2.8x to be exact) slower in overall applications performance than an ideal RAM SSD with similar MB/s throughput.
  
  ...Later:- I was wrong about this one.
  
  Violin Memory designed a flash SSD with balanced random R/W IOPS in Q4 2008 using a combination of factors.
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  • over-provisioning and fast garbage collection ensured a constant flow of pre-erased flash.
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  • their non blocking RAID RAM cache architecture enables a read to be done from a virtual flash block while an erase-write is still in operation on the same flash block.
  
  
  And in April 2009 - SandForce published - Fact or Fiction - all flash SSDs have unbalanced R/W performance . This is one of a set of articles which discuss design factors inside their small form factor SSD controller.

• Prediction 4 - Latency in flash SSDs will not scale in the same way as throughput, and will always be significantly worse than that in ideal RAM SSDs.
  
  The ratio of read access times for RAM SSDs compared to flash SSDs may improve for a few years (as the gap gets smaller) but then it will hit a brick wall - and may in fact get worse again.
  
  The reason is - that flash SSDs have not yet been optimized for latency - so there is some scope to reduce the latency gap with RAM systems (which have already been highly optimized).
  
  But in future product generations as flash SSDs increase in density - a read or write cycle becomes an increasingly complicated on-chip process - which includes calibration, error correction and address translation all being done by controllers between the memory array and the host interface controller or card data bus.
  
  This series of steps (to do a simple read) will diverge from what happens in a typical RAM to the point where flash and RAM look like completely different species. That's unlike earlier generations of flash in which the read cycle looked the same as a static RAM - but simply took longer.

• parallelization of the internal media arrays

• improved media management technology.
  
  MFT from EasyCo is a software solution which has already been mentioned above. But the same algorithms could be run in the SSD hardware.
  
  Another licensable solution - which is already being developed at the chip level is IOP Buster architecture from Link_A_Media Devices

• faster media controllers

• faster host interface controllers (and faster interfaces driven by the needs of the SSD market rather than adapted from the HDD market)

• hybridizing on board memory technologies - for example using faster RAM-like non volatile memory in some parts of the device and slower flash-like memory in the bulk storage arrays

• the Fastest SSDs - updated regulalry - this gives the state of the art in popular form factors.

• Understanding Flash SSD Performance (pdf) - by Douglas Dumitru, CTO EasyCo LLC is a reference for systems engineers who want to understand the dynamics of flash versus hard disk performance running real applications.

• the Problem with Write IOPS - in flash SSDs - Random R/W IOPS data for flash SSDs is a poor predictor of likely application performance in some common types of enterprise server applications.

• Flash in the Enterprise (pdf) by Jamon Bowen, Texas Memory Systems describes some the properties of Flash memory and then explains how their RamSan-500 product leverages its strengths and compensates for its weaknesses to offer the fastest enterprise ready rackmount Flash SSD system.

• Design Tradeoffs for (SLC flash) SSD Performance (pdf) by Nitin Agrawal, Vijayan Prabhakaran, Ted Wobber, John D. Davis, Mark Manasse and Rina Panigrahy looks in detail at the internal architecture of a typical commercially available SLC flash SSD and the various points where choice of software algorithms can impact performance.

• Calling for an End to Unrealistic SSD vs HDD IOPS Comparisons - an editor's plea to SSD vendors.

• New Equations for Measuring the Value of High Performance Storage (pdf) - by Tomas Havrda and Chas Chesler, Solid Access Technologies, compares the rack height, electrical power and price to achieve identical IOPS using RAM SSDs and hard disks.

• Why I Tire of - "Tier Zero Storage" - You don't need to waste any of your precious brain cells by investing "tier 0 storage" with an importance this travesty of storage jargon really doesn't deserve.

• Supercapacitors for SSD backup power - describes how write speed and endurance can be optimized by protecting cache memory in a flash SSD with ultracaps. This is a technique which was pioneered in the SSD market by DTS and Memoright.

• SSD Market History - lists key market, business and technology milestones in the 30 year history of the SSD market.