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Texas Memory Systems discusses MLC and RAM in enterprise SSDs

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why does TMS still favor SLC for enterprise accelerator SSDs?
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 derivatives traders.

TMS has been selling high speed enterprise SSDs longer than anyone else in the industry - and for years has been the highest ranking rackmount SSD company in StorageSearch.com's quarterly Top 10 SSD Companies List.

I approached the company to ask about 2 issues which occupy a lot of thinking in the top end of the SSD market:-
  • what's the role of MLC flash versus SLC, and
  • what's happening in the market with RAM SSDs?
I started by saying that among enterprise SSD makers - TMS now seems like one of the few companies which doesn't include MLC in their server SSD product line.

Leading the MLC enterprise tide - Fusion-io has been pushing its MLC based PCIe SSDs into server apps since 2007. And and since 2009 SandForce has been offering its SSD oem partners (now numbering over 20 companies) an easy to integrate controller technology which manages data integrity and endurance to a degree which enables intensive write IOPS SSDs using MLC - to last for 5 years. And more recently - in September 2010 - a year after shipping its first enterprise SLC only SAS SSDs - Pliant Technology reacted to market demand and started offering customers MLC variants.

So I asked Jamon Bowen - what's going on? What's TMS policy about MLC SSDs?

Bowen said I was right in thinking that the company doesn't ship any MLC SSDs. Its market is at the high end of the SSD performance range. As a company - he said TMS has evaluated and used more types of memory technology than anyone else in the market. And they have also evaluated consumer grade MLC.

He mentioned several related reasons for not using MLC right now in their SSD products.

He said current consumer grade MLC nand flash has endurance on the order of 3,000 write cycles. Although it would be possible for TMS to design an ASIC controller with heavy use of over provisioning and parallelism (which would cut down the average latency and extend SSD life) the cost of doing this - at the high end of the performance spectrum (and in the legacy SSD market where the flash management is transparently offloaded from the host) - would nibble away at the native cost advantages of the cheaper MLC. He said the end result would be a rackmount MLC SSD that was only 50% cheaper than using SLC. And another problem would be that the company's burn-in process (done for QA as part of manufacturing) would use up 10% of the endurance life before the SSD even reached the customer.

Bowen said that new types of so called "enterprise MLC flash" - which use enhanced cell programming circuitry in the chip design - might shift the balance of the viability equation. He said that customers would not see consumer grade MLC based SSDs from TMS in the next couple of years. On the other hand he said that TMS is interested in eMLC and its engineering team can move quickly to bring products to the market.

I said I was surprised by how popular - articles about flash endurance - had become with the readers of StorageSearch.com - considering that readers have to get engaged with semiconductor and architectural complexities to follow the arguments.

Jamon Bowen said if users were fixated too much on wear out - they might not realize that other factors in SSD design could contribute just as much or more to SSD failure.

On the subject of SSD technology education - in a follow up email Jamon Bowen suggested - "It might be a worthwhile endeavor to start educating the reader base on the difference between eMLC and MLC as I expect that across the market vendors will be highlighting eMLC vs MLC in a similar way that SLC and MLC are compared today."

Later:- In December 2011 - I spoke to Holly Frost, CEO and Dan Scheel, President of Texas Memory Systems about their new fault tolerant SSDs, what's going on in the SSD market, and the philosophy that steers the design of their SSDs. You can see details in the article - "StorageSearch talks SSD with Holly Frost."
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Other Views about MLC versus SLC & enterprise flash
Editor:- companies like Fusion-io (the best known maker of PCIe SSDs) and SandForce (the best known maker of SSD controllers) have been enthusiastic supporters of the concept of using MLC flash (instead of the more expensive SLC) in heavy duty mission critical enterprise accelerator SSDs. And they have developed technologies which make this feasible from the reliability and performance point of view.

The articles below reveal more about their thinking in this area.

Fusion-io's CEO - discusses MLC SSDs in banks

SandForce's CEO - SSD Bookmarks

Texas Memory Systems' CEO - discusses SSD design

the new SSD uncertainty principle - resetting the assumptions about enterprise MLC flash - taking a look at STEC's CellCare
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Megabyte spent another pleasant day
shooting the breeze about SSDs.
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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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Other Views About RAM in SSDs
Editor:- my classic article RAM SSDs versus Flash SSDs - which is Best? includes views from about 10 different companies in the industry.

My article - RAM Cache Ratios in flash SSDs - shows the huge differences in thinking about the use of RAM cache in flash SSDs.

And this is just one of many issues which I have called - the SSD Heresies.
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