MLC

How Controllers Maximize SSD Life – Improved ECC

Tempus FugitError correction (ECC) can have a very big impact on the longevity of an SSD, although few understand how such a standard item can make much difference to an SSD’s life.  The SSD Guy will try to explain it in relatively simple terms here.

All NAND flash requires ECC to correct random bit errors (“soft” errors.)  This is because the inside of a NAND chip is very noisy and the signal levels of bits passed through a NAND string are very weak.  One of the ways that NAND has been able to become the cheapest of all memories is by requiring error correction external to the chip.

This same error correction also helps to correct bit errors due to wear.  Wear can cause bits to become stuck in one state or the other (a “hard” error), and it can increase the frequency of soft errors.

Although it is not widely Continue reading

How Controllers Maximize SSD Life – External Data Buffering

Tempus FugitSince NAND flash is weakened by erase/write cycles then it would make sense to try to reduce those cycles to prolong the life of an SSD right?  That’s what external data buffers are designed to do.

There are many ways to use RAM (either a RAM internal to the SSD controller chip or a discrete DRAM chip on the SSD’s printed circuit card) to stage data in a way that will reduce erase/write cycles.

One is to perform a function called “Write Coalescing.”  This involves Continue reading

Samsung Introduces TLC SSD

This Graphic Illustrates the Challenge of TLC FlashSamsung on Monday introduced a new “840” SSD series which reviewers have found is based on TLC flash.

Oddly enough the press release for this product seems only to have been distributed in Korea to reviewers who attended a special introduction of the device.  The SSD Guy has not been given the specifications presented at the event, and had to ask Samsung for a copy of the press release.

The press release focuses on the product’s 100,000 read IOPS, that it comes in two versions, the “Pro” model for the enterprise and another model for client applications, and the fact that the controller uses a new design based on three ARM cores. A read IOPS figure of 100,000 is very high performance for a SATA drive!  One has to wonder if the client market will be able to distinguish between this level of performance and drives with fewer than 10,000 IOPS.

Other specifications Continue reading

How Controllers Maximize SSD Life – Better Wear Leveling

Tempus FugitIn this post we will explore how the right wear leveling algorithm  can help a controller maximize the life of an SSD.

Wear leveling is a fact of life with NAND flash – blocks start to suffer bit failures after a certain number of erase/write cycles (usually specified from the thousands to the hundreds of thousands) and it is only natural that software will attempt to over-write some blocks more than others.  In order to prevent this from causing failures, all of today’s SSD, USB flash drive, and flash card controllers incorporate some sort of wear leveling.

This is a simple re-mapping of the contents of the flash chips.  A more graphical explanation is Continue reading

How Controllers Maximize SSD Life

Tempus FugitHow do controllers maximize the life of an SSD?  After all, MLC flash has a lifetime of only 10,000 erase/write cycles or fewer and that is a very small number compared to the write traffic an SSD is expected to see in a high-workload environment, especially in the enterprise.  Still, MLC is becoming the norm in the enterprise.

How do they do that?

This is where SSD architects really earn their pay.  There are eight basic techniques that The SSD Guy knows of to extend SSD life beyond Continue reading

SMART Optimus Ultra+ SSD: SLC Performance Using MLC Flash

SMART Guardian vs Normal Flash Management - More good BlocksSMART Storage Systems has introduced a new enterprise-class SSD that the company says: “increases the endurance of cMLC Flash to a level that makes SLC drives obsolete.”  That’s a pretty hefty claim!

The new Optimus Ultra+ SSD is specified at 100K read IOPS and 60K write IOPS, through its 6Gb/s SAS interface.  With capacities ranging from 100-800GB, this SSD supports up to 50 full drive writes per day over its 5-year lifespan, double that of the company’s Optimus Ultra which was introduced in February.  That’s quite something for an MLC-based SSD.

SMART has tapped into its Guardian technology to reap SLC benefits from MLC flash through both enhanced external and internal algorithms.  Like all other SSD makers and SSD controller makers SMART has focused a lot of attention on error correction, DSP, and other means of correcting errors externally to the flash.  The company has also partnered with Continue reading

Not all SSDs are Created Equal

Results of the SNIA PTS on Seventeen SSDs and one HDDSSDs vary widely in performance.  This is something that becomes amazingly clear when a number of these devices are put through a battery of tests.

Calypso Systems ran the SNIA SSD Performance Test Specification (PTS), outlined in an earlier post in this blog, on seventeen SSDs and a single HDD.  The results appear, in miniature, in the graphic for this post. Continue reading

Contact

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

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