SSD Reliabiity

What’s In My SSD? SLC, MLC, or TLC?

SLC, MLC, or TLC?Someone recently asked The SSD Guy if there is a way to determine whether an SSD is SLC, MLC, eMLC or TLC.

I found it a little odd to be asked this, since most vendors tell what kind of flash they use in an SSD’s specifications, especially if it’s SLC.

Not finding it there then the next thing I would look at is the price.  Raw SLC NAND flash now sells for about 6-10 times as much as its MLC counterpart, so an SSD with a price of around $1/GB is likely to be MLC and one that sells for around $10/GB is probably SLC.

TLC SSDs are really rare.  There is the 840 from Samsung and the Ultra II and X300 from SanDisk.  It’s also pretty rare to find an SSD that is based on eMLC, because eMLC achieves its higher endurance by slowing the part down.  There are other, better ways to extend endurance.

Now that you know all this, please note that the kind of flash used to produce the SSD is probably unimportant.  Certain MLC SSDs outperform some SLC SSDs, both in speed and in endurance – it all has to do with the quality of the controller.  Some useful comparisons of SLC and MLC SSD performance are in the post: “Not All SSDs are Created Equal“.  There’s a thorough explanation of controller techniques in The SSD Guy’s series on SSD controllers.

Furthermore, NAND chips allow controllers to change flash pages inside the chip from TLC to MLC to SLC as needed, so some SSDs actually internally manage hot data to SLC and cooler data to MLC or TLC.

For those that have read this far, I would recommend changing your focus away from questions of SLC vs. MLC vs. TLC and focus instead upon the SSD’s published specifications (like speed and endurance) and on its SMART attributes.  The SMART attributes will always tell you how your SSD is wearing, and the specifications will tell you how it is expected to perform.

If you don’t trust the manufacturer’s performance specifications, then I highly recommend using the SNIA performance test specification, which gives unbiased performance results for any SSD.

LSI SandForce SSD Controllers Move the Knee in the Curve

LSI SandForce SF3700 Controller DuraWrite ImprovementsLSI’s SandForce has just rolled out its SF3700 family of four SSD controllers aimed at the Entry Client, Mainstream Client, Value Enterprise, and Enterprise Storage marketplaces. Performance is impressive, with worst-case random PCIe IOPS at 150K read/81K write and 94K/46K for the SATA interface.

The SF3700 family builds on the division’s first two product families by adding a choice of PCIe or SATA interfaces, LDPC error correction, and a boosted set of flash management features.  The SSD Guy will explore this last point after highlighting the other two.

By providing both PCIe and SATA interfaces LSI is directly addressing the future: PCs are aiming to move to the m.2 SSD specification rather than Continue reading

Solving SSD Power Spike Issues

The following guest post was contributed by Doug Dumitru the CTO of Easy Computing Company (EasyCo), a software R&D company which develops and markets SSD performance enhancement solutions

Doug Dumitru, EasyCoIt would appear that you could build an all-SSD array by simply replacing all of the HDDs in a cabinet with SSDs.  I tried that and ran into some surprising issues that were very confusing at first.

SSD spec sheets, might lead you to believe that power is just not an issue.  For example, Samsung lists the power use for a 512GB 830 SSD at 0.127W (typical) for “Active Power Use”.  This implies very low demands on the system power supply.

If you do some more research, you find that the peak power usage is a lot higher.  AnandTech, in a review article reports sequential write power draw at 5.14W and random write power draw at 5.8W. In that 2.5” SSDs use the 5V power rail exclusively, this is more than Continue reading

Webinar: Flash Best Practices

I had the opportunity to participate in a round table webinar covering the best practices for solid state storage on July 18.  The hour-long session (including Q&A) can be replayed at BrightTalk.

In this round table webinar entitled Best Practices for Solid State Storage Implementation storage analyst Tom Coughlin moderated three of us, Radoslav Danilak of Skyera, Esther Spanjer of SMART Storage Solutions, and The SSD Guy (Yours Truly) in a Continue reading

Kaminario’s Performance and 7-Year Flash Life Warranties

Kaminario LogoToday Kaminario added a performance guarantee and a 7-year warranty to its arsenal.  The company introduced its “Consistency Under Failure Guarantee” which ensures customers will see no more than a 25% drop in performance during a system failure.  This means that critical operations and applications can continue to run at near-standard performance despite the failure of an SSD or even an entire node.  Kaminario president Dani Golan told The SSD Guy last week that this is a conservative guarantee, and that few customers see more than a 10% degradation during failure tests in their own production systems.

As for the 7-year flash endurance warranty, no matter which SSD Continue reading

Are HDDs Vibration Sensitive?

Brendan Gregg in Sun's Fishworks Lab shouting at an HDD arrayOne reason to use SSDs is that, with no moving parts, these devices are insensitive to shock and vibration.  HDDs, on the other hand, are sensitive enough to vibration that it can cause access delays.

How sensitive are they?  Well, I have seen some overblown claims from SSD makers that shock will cause HDD head crashes.  I am not sure that I believe such claims, but I certainly do believe that an HDD’s actuator (the read/write head mechanism) can be shaken away from its track, causing a Continue reading

LSI’s Take on Data Center Flash

LSI Corporation LogoLSI Corp. has launched a new blog that covers (among other things) flash storage.  It’s only natural – the company’s SandForce subsidiary is riding high on the SSD wave and LSI’s HBAs are finding widespread use, both internally and externally, in the production of two-hop PCIe SSDs.

A recent post called “What are the Driving Forces Behind Going Diskless” by LSI Fellow Rob Ober outlines the leading Continue reading

SSDs and TCO

Shed some light on your SSD decisionOne of the best arguments to use an SSD is also one of the most difficult ways to sell anything.  This is the Total Cost of Ownership, commonly abbreviated to “TCO.”

TCO has been used as an argument for buying anything from compact fluorescent bulbs to Jaguar automobiles.

The argument usually revolves around an item whose initial price is higher, but which has lower ongoing (or operating) costs, and when these costs are combined, the higher-priced item proves to cost less to own over the long run.  In the case of a compact fluorescent (CF) bulb, the bulb may cost $7, versus $1 for an incandescent bulb, but it consumes 18 Watts compared to the 75 Watts consumed by the incandescent bulb it replaces.  In addition the CF bulb lasts ten times as long (10,000 hours vs. 1,000 hours.)  This works out to a savings of 470 kWh – or about $50 – plus $3 in bulb costs. Continue reading

Extreme SSD Error Correction

Chuo University EmblemAt last week’s International Solid State Circuits Conference (ISSCC) Shuhei Tanakamaru, a researcher from Japan’s Chuo University, detailed a scheme to reduce MLC SSD bit error rates (BER) by 32 times over conventional techniques.  The approach used an impressive combination of mirroring, vertical and horizontal error correction, and a deep understanding of the most likely kinds of bit errors flash will experience.

This is a very novel and well-conceived technique that may find industry adoption in future SSDs.

The steps included in the paper are used in addition to the Continue reading

SSDs that Don’t Wear Out

The End of NAND Flash Wear?This is a bad day for The SSD Guy.  I just finished publishing an eight-part series explaining How Controllers Maximize SSD Life, then my evil twin The Memory Guy today published a post telling of a new flash design from Macronix that might just eliminate the flash wear-out mechanism!

But my concerns are inconsequential compared to the feelings of all those folks who have devoted phenomenal time and energy to develop wear management algorithms.

This all stems from an article in the IEEE Spectrum that details a flash chip design that Continue reading

Contact

Jim Handy
Objective Analysis
SSD Market Research
+1 (408) 356-2549
Jim.Handy (at) Objective-Analysis.com

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