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RAM SSDs

"Far from being killed by flash SSDs - the high-end RAM SSD market grew in 2010 and then again in 2011" says editor Zsolt Kerekes.

"Every time the PCIe flash SSD market sells another 50 to 100 cards to accelerate a bunch of user servers - that creates a new demand bottleneck which may one day be cleared only by RAM SSDs."

Despite that the enterprise SSD market today - which 10 years ago was 100% RAM based - is now overwhelmingly dominated by flash. Reports from SSD vendors suggest that in 2012 - RAM SSDs and RAM cache in flash SSDs probably accounted for no more than 1 to 2% of all enterprise SSD capacity.
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When flash SSDs aren't fast enough!
RAM based SSDs are the original type of solid state disk and have been around for decades.

They rely on batteries to retain data when power is lost. Most models also include internal hard disk drives to which data is saved under battery power, so that data is not lost when the battery runs down. This hybrid technology means that RAM based SSDs are more bulky than flash counterparts and RAM SSDs are unable to operate in the same range of hostile environments.

RAM based SSDs are mostly used in enterprise server speedup applications. The fastest RAM SSDs are faster than the fastest flash SSDs. But for many server speedup applications flash SSDs are fast enough.

Unlike flash SSDs, RAM based SSDs never had restrictions on the number of write cycles. That made them more popular in enterprise acceleration applications in the past. But write endurance problems may be a thing of the past for flash.

Like hard disks - RAM SSDs have symmetric read/write IOPS. That's another big difference between RAM and flash SSDs.

The fastest flash SSDs available in 2009 had achieved parity between random read and write IOPS.

But that's not how transaction based applications work. The important differentiator here is repeat again write IOPS. If you compare that between RAM and flash based SSDs - the RAM SSDs are upto 100x faster - even when the datasheets suggest they look the same.

On the other hand - in some enterprise applications - like IPTV servers - the random write IOPS rarely repeats in the same memory space during milli-second timeframes - and in these video server apps - flash really does perform as well as RAM - and is much cheaper.

Latency figures quoted by many flash SSD products can also look very similar to those for RAM SSDs. But low random write latency doesn't mean that the data has actually hit the flash media yet - as you'll find if you try to read back the data and rewrite to the same block.

There are also some non volatile memory products such as PRAM, FRAM and RRAM which are replacing flash in industrial applications - and which already offer 1 to 1 read/write performance. But their capacity is 2 orders of magnitude too low to be of use in server applications.

RAM SSDs cost about 3x as much as SLC flash SSDs for similar capacity in FC SAN rackmount systems - (based on pricing data 2011.)

The ideal choice of SSD depends on the specific server and application environment and cost / benefit analysis.

Not everyone needs or can afford the fastest SSDs. Some environments do. Others don't.

Identifying the right choice of SSD in the right place is a complex decision - which requires a high degree of SSD education and trust in the vendor.

More articles about the problems and solutions related to accelerating enterprise server apps can be seen on the SSD ASAPs page.
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how fast can your SSD run backwards?
Editor:- April 20, 2012 - StorageSearch.com today published a new article which looks at the 11 key symmetries in SSD design.

SSDs are complex devices and there's a lot of mysterious behavior which isn't fully revealed by benchmarks and vendor's product datasheets and whitepapers. Underlying all the important aspects of SSD behavior are asymmetries which arise from the intrinsic technologies and architecture inside the SSD.

Which symmetries are most important in an SSD? - That depends on your application. But knowing that these symmetries exist, what they are, and judging how your selected SSD compares will give you new insights into SSD performance, cost and reliability.

There's no such thing as - the perfect SSD - existing in the market today - but the SSD symmetry list helps you to understand where any SSD in any memory technology stands relative to the ideal. And it explains why deviations from the ideal can matter.
SSD symmetries article The new article unifies all SSD architectures and technologies in a simple to understand way. ...click to read the article
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RAM vs flash SSDs decision tipping point
Editor:- in December 2010 - I interviewed Jamon Bowen, Director of Sales Engineering for Texas Memory Systems and asked him about the use of SSDs in financial applications like banks and traders - a market which he said accounts for most of their RAM SSD sales.

The company which started in RAM SSDs over 30 years ago - now sells more flash SSDs than RAM SSDs (even though the product brand for both types of SSD is confusingly called RamSan.) Bowen said that flash is 70% of their business.

Jamon Bowen said that in many bank applications RAM SSDs are actually cheaper than flash - because of the small size of the data. TMS still sell a lot of 16GB RAM SSDs.

Production bank systems are typically shared by many hosts and get a lot of write IOPS / capacity. To achieve the same reliability and latency with flash would require over provisioning which would drive the cost up.

He suggested a simple rule of thumb for intensive IOPS bank SSDs on the SAN
  • < 128GB capacity - RAM SSDs cheaper
  • 128GB to 4TB capacity - middle ground could be either - or determined by other constraints
  • > 4TB - flash SSDs cheaper
Jamon Bowen said that the analysis side of operations in banks is different. That tends to have much larger data sets and is more read than write intensive. In these apps - flash SSDs are usually more economic.

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how will Memory Channel SSDs affect the PCIe SSD market?

Editor:- April 29, 2013 - StorageSearch.com today published a new article about the technical challenges and market opportunities posed by Memory Channel Storage SSDs which are being designed by SMART and Diablo Technologies. ...read the article


in memory database even better with FIO's flash

Editor:- November 20, 2012 - McObject recently released new benchmark results which indicate that the in-memory database company is not so unfriendly to flash SSDs as you may have thought from reading earlier company positioning papers.

It seems that a software product - which was originally designed for the DRAM-HDD world - is a good fit in the flash SSD world too - if you have the right scale of data and the right SSD. ...read more


Micron sources power holdup technology for NVDIMMs

Editor:- November 14, 2012 - Micron has signed an agreement with AgigA Tech to collaborate to develop and offer nonvolatile DIMM (NVDIMM) products using AgigA's PowerGEM (sudden power loss controller and holdup modules).


STEC discloses RAM vs flash SSD revenues

Editor:- November 7, 2012 - among other things STEC revealed yesterday in its earnings conference call that RAM SSDs were approximately 4% of its revenues in the recent quarter.


AMD will rebrand Dataram's RAMDisk software

Editor:- September 6, 2012 - Dataram today announced it will develop a version of its RAMDisk software which will be rebranded by AMD in Q4 under the name of Radeon RAMDisk and will target Windows market gaming enthusiasts seeking (upto 5x) faster performance when used with enough memory. See also:- SSD software


Kaminario recommends you read SSD Symmetries article

Editor:- June 15, 2012 - I accidentally discovered today that earlier this week Gareth Taube, VP of Marketing at Kaminario published a new blog in which he recommends my article about SSD Symmetries.

Gareth says "Flexibility, such as being able to integrate multiple memory technologies into a single box (like Kaminario's K2-H), is going to be increasingly important to customers who want efficiency and customization options. This is especially true because there are many memory innovations coming on the near horizon." ...read Gareth's blog

Editor's comments:- when I was writing the symmetry article one of the things I had in mind to do was to put more examples in it. Then I realized that having lots of examples would simply make the article unreadable.

One of the examples I was going to use for good roadmap symmetry (but then forgot to put anywhere) was in fact Kaminario - because they can leverage off whatever Fusion-io does with flash (or other nv memory) and furthermore Kaminario can also leverage off whatever server makers do with CPUs and RAM. Roadmap symmetry is a long term consideration - important for big users who don't like supplier churn and important for VCs and investors too.

...Later:- I'm glad I wrote that bit about "roadmap symmetry" - because by a spooky coincidence - 3 days later we got the news that Kaminario's investors still love what they do.

June 18, 2012 - Kaminario today announced it has secured a $25 million series D round of funding, bringing its total funding to $65 million.


sharpen your SSD R/W grid latency weapons to 5µS

Editor:- May 9, 2012 - Kove has published some new record latency numbers for its fast RAM SSD - the XPD L2 - which has achieved continuous and sustained 5 microsecond random storage read and write when connected via 40Gb/s InfiniBand adapters from Mellanox .

Kove's system has good R/W symmetry which the company says - is not subject to periodic performance jitter or "periodicity". Even under constantly changing disk utilization, it delivers uniform, predictable, and deterministic performance.

"The Kove XPD L2... allows high performance applications to use storage as a weapon rather than accept it as a handicap," said Kove's CEO, John Overton. "We are pleased to set a new bar height for storage latency."


STEC's RAM SSDs percentage?

Editor:- February 28, 2012 - "Our DRAM-related products accounted for 3% of revenue" said Raymond Cook, CFO, STEC - in the company's Q4 2011 - earnings conference.


Kaminario's systems today are mostly flash

Editor:- February 7, 2012 - Here's an update on the long running RAM versus flash transition in enterprise SSD accelerators.

It's about 20 months since Kaminario entered the SSD market as a new name in the RAM SSD market - and just 6 months since the company also started offering flash - as a hybrid or pure alternative - based on PCIe SSDs from Fusion-io.

Yesterday I asked Kaminario's VP of marketing - Gareth Taube how's the flash thing going? And can you tell me and my readers what proportion of recent system shipments are flash rather than RAM.

He told me - "I would say we are running about 45% all flash arrays, 45% Hybrids (but the hybrids are mostly Flash with 10% DRAM) and about 10% all DRAM. At least that is the way it has been running in the last 2 quarters."


Fusion-io's 1 billion IOPS demo narrows latency gap between flash and RAM SSDs

Editor:- January 6, 2012 - in a historic demo yesterday showing the capabilities of its latency reducing Auto Commit Memory (ACM) extension Fusion-io announced it had exceeded 1 billion IOPS (64 byte data packets) in a configuration which used 8 HP servers each configured with 8x ioDrive2 Duo PCIe SSDs.

Editor's comments:- although we're used to thinking about SSD IOPS in terms of bigger packets - such as 4kB - instead of the very small packet size in this demo - IOPS is simply a convenient and not always reliable way of comparing the relative performance of storage products.

In real life - users don't have a choice of what size the R/W operations are which take place in their apps. They occur at all sizes (mostly smaller than 4kB) and when these R/W operations take place in traditional storage architecture systems - which internally impose their own restrictions on the minimum size of atomic data packets - that's where latencies and performance become discontinuous compared to the value of the data update due to amplification and packetization effects.

In my view - the important thing about this demo - is that the same PCIe SSD product which can perform useful work as a storage device - can also be deployed as a super scaler memory device - when it is running the appropriate software.

The difference is that with traditional storage software - you might expect that a 64x PCIe SSD system might hit 64M IOPS or some similar figure (regardless of the small size of the data packet). Instead the demo shows that apps developers can get 16x more performance in small R/W transactions if they are willing to invest the effort to make their apps work with FIO's new APIs.

It's that order of magnitude difference which is the attraction for some markets - because it closes the gap in performance between RAM SSDs and flash SSDs. And when you can run apps 10x faster than other flash competitors at the same price - or support 10x bigger data sets than competitors using RAM SSDs - that create new markets. See also:- Record Breaking Storage

new article on RAM SSDs

Editor:- April 22, 2011 - Long Live RAM SSD is a new article by Woody Hutsell which reflects on how the RAM SSD market - which many observers once believed would be killed by flash - has got a great future.

the Fastest SSDs
the Top 10 SSD Companies
RAM Cache Ratios in flash SSDs
Why I Tire of - "Tier Zero Storage"
RAM versus Flash SSDs - which is Best?
the new way of looking at Enterprise SSDs
Introducing the concept of RAMClouds (pdf)
when the SSD brand sends the wrong signal - RamSan and Dataram
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Surviving SSD sudden power loss
Why should you care what happens in an SSD when the power goes down?

This important design feature - which barely rates a mention in most SSD datasheets and press releases - has a strong impact on SSD data integrity and operational reliability.

This article will help you understand why some SSDs which (work perfectly well in one type of application) might fail in others... even when the changes in the operational environment appear to be negligible.
image shows Megabyte's hot air balloon - click to read the article SSD power down architectures and acharacteristics If you thought endurance was the end of the SSD reliability story - think again. ...read the article
RAM based SSDs - image shows Megabyte ramming his way into the cheese store
sometimes you just can't wait

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RAM based SSD makers list
ACARD Technology

Attorn

Avere Systems

Curtis

Curtiss-Wright

Dataram

Density Dynamics

DDRdrive

Dynamic Solutions International

Kaminario

Kove

Real Ram Disk

Solid Access Technologies

Solid Data Systems

STEC

Texas Memory Systems

Third I/O

TiGi

Violin Memory

ViON
There used to be many other RAM SSD companies at earlier stages in SSD market history - for example Cenatek, Imperial Technology and Platypus Technology - which are no longer in business.
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the Problem with Write IOPS in flash SSDs
Random "write IOPS" in many of the fastest flash SSDs are now similar to "read IOPS" - implying a performance symmetry which was once believed to be impossible.

So why are flash SSD IOPS such a poor predictor of application performance? And why are users still buying RAM SSDs which cost an order of magnitude more than SLC? (let alone MLC) - even when the IOPS specs look superficially similar?

This article tells you why the specs got faster - but the applications didn't.
the problem with flash SSD  write IOPS And why competing SSDs with apparently identical benchmark results can perform completely differently. ...read the article
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