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SanDisk readies better format for SSDs

Posted: 07 Nov 2008 ?? ?Print Version ?Bookmark and Share

Keywords:flash drive? SSD? NAND?

SanDisk Corp. will be launching a new flash-file format for solid-state drives (SSDs) in its 2009 products, claiming it bolsters performance 100-fold on some operations. It will also be releasing details on two metrics for comparing the performance of SSDs.

The company has no plans to license the ExtremeFFS file system so far, despite that the past TrueFFS format from MSystems, which SanDisk acquired in 2006 was widely licensed. It is however updating to make its new measures for SSD performance and endurance broadly accepted.

ExtremeFFS seeks to improve sequential write performance by giving a direct route to writing individual pages of data. Rather than having a system to update and move an entire block at a time, Extreme FFS can simply write a new page to a new block and invalidate the old page.

Innovative features
The file system handles garbage collection simultaneously with read and write in multiple nonblocking channels. It can also identify data structures that are most and least often accessed and optimize the placement of the data sets.

The sequential write issues were relatively small for digital cameras and other devices that have used NAND flash cards to date. But Windows PCs typically need many sequential random write operations that can increase significant performance issues for SSDs.

"ExtremeFFS should not only improve performance on random read and write operations, but reduce power use and upgrade flash endurance as well," said Don Barnetson, senior director, marketing, SanDisk's SSD group.

"Most of our competitors don't like to talk about what's going on inside their drives, but we are trying to be more open about it," he added.

The past generation TrueFFS format was used for Personal Computer Memory Card International Association flash cards in Microsoft Windows 95 and became widely licensed by flashcard makers. SanDisk had royalty revenues of $450 million in 2007 based on licenses that companies took for its multiple patents, including those on TrueFFS.

While SanDisk currently has no plan to license ExtremeFFS, it is encouraging the industry to adopt two new SSD metrics to communicate performance characteristics to end users.

Virtual RPM (vRPM) is a method for calculating the performance of an SSD in the equivalent of rotation figures used to measure hard drives today. The equation considers the different reads and writes performance characteristics of flash, as well as the typical mix of reads and writes in average PC applications.

"vRPM answers the question: How fast would you have to spin a virtual hard drive to achieve the level of performance seen by an SSD in a client PC?" said Rich Heye, general manager, SanDisk's SSD group in a press statement.

The company has posted details about the vRPM approach at its Website.

"There are so many axis of performance that it's difficult to measure the relative performance of SSDs today," said Barnetson. "Our goals are to get the industry to adopt this metric and to be transparent about how it works," he added.

The value of SSDs
"There has been a deluge of SSD products with varying levels of quality that have created undeserved hype and confusion," said Joseph Unsworth, research director, Gartner Inc., in a press statement. "Industry support behind a common metric that clearly articulates the value proposition of an SSD on a like-for-like basis to a HDD will be instrumental in driving end-user understanding and subsequent adoption of SSDs," he added.

A second metric announced earlier this year give a means to gauge the endurance of SSDs, an important aspect of the devices. Unlike hard disk media, which do not degrade significantly over typical product life spans, the flash cells in SSDs can wear out before a product reaches its end of life.

SanDisk has written a white paper on its so-called long-term data endurance metric. It submitted the paper recently to the Jedec 64.8 working group that is developing standards for SSDs.

- Rick Merritt
EE Times

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