SSD Reliabiity – Page 4 – The SSD Guy Blog

How Controllers Maximize SSD Life – External Data Buffering

Since 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 “How Controllers Maximize SSD Life – External Data Buffering”

Samsung Introduces TLC SSD

Samsung 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 “Samsung Introduces TLC SSD”

How Controllers Maximize SSD Life – Better Wear Leveling

In 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 – Better Wear Leveling”

How Controllers Maximize SSD Life

How 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 “How Controllers Maximize SSD Life”

SMART Optimus Ultra+ SSD: SLC Performance Using MLC Flash

SMART Guardian vs Normal Flash Management - More good Blocks SMART 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 (DWPD) 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 “SMART Optimus Ultra+ SSD: SLC Performance Using MLC Flash”

Standards for SSD Endurance

SSD endurance is an important concern that stands in the way of SSD adoption in a number of data centers. Since flash is new to the enterprise (and computing systems are a new market for flash) important issues including wear specifications still need to be hammered out.

Until flash SSDs started experiencing adoption in standard computing environments, nobody really anticipated the difficulties that would arise from flash’s inherent wear-out mechanism. Most flash manufacturers erroneously believed that Continue reading “Standards for SSD Endurance”

What Happens when SSDs Fail?

There’s a lot of “Fear, Uncertainty, and Doubt” – FUD – circulating about SSDs and their penchant for failure. NAND flash wears out after a set number of erase/write cycles, a specification known as the flash’s endurance.

While some caution is warranted, a good understanding of how SSDs really behave will help to allay a lot of this concern. Continue reading “What Happens when SSDs Fail?”

SSDs and RAID

The SSD Guy has been asked a number of questions lately about SSDs and RAID. Most of these center around the difference in failure behaviors between SSDs and HDDs – HDDs fail randomly (if ever), while SSDs fail relatively predictably due to wear.

Oddly enough, SSD failures due to wear make them a little friendlier than HDDs. The wear mechanism is managed by the controller in the SSD. SSDs have spare blocks, and the controller manages those blocks, so the controller understands exactly how much wear the SSD has undergone and how much room is left before the SSD will start to have difficulties. Continue reading “SSDs and RAID”