Analysis: SSD performance -- is a slowdown inevitable?

How well an SSD performs over time depends on the firmware, controller

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Intel isn't alone when it comes to performance issues. Computerworld recently tested a consumer-grade 120GB SSD from OCZ Inc. Initial tests using the ATTO Disk Benchmark tool showed excellent read and write speeds of 230MB/sec. and 153MB/sec., respectively. But a second test showed that the read/write speeds had dropped to about 178MB/sec. and 80MB/sec., respectively. OCZ admits its Apex SSDs use a controller made by Taiwanese-based JMicron Technology Corp., which is known to have issues with random write performance and it can play havoc when a user is multitasking on a computer. An OCZ spokeswoman suggested customers visit its "very popular" community forum, which offers "plenty of tweaks and workarounds for users to optimize their drives."

Computerworld recently tested a consumer-grade 120GB SSD from OCZ Inc. The initial tests using the ATTO Disk Benchmark tool showed excellent read/write speeds of 230MB/sec. 153MB/sec., respectively.
The first benchmark test shows read/write speeds comparable with the vendor's specifications.
Computerworld immediately retested the drive, the read speed dropped to about 178MB/sec. and writes plummeted to about 80MB/sec
Read/write speeds drop significantly in the second benchmark test

Synthetic workloads like those produced by benchmarking software are typically not a real-world test of a drive performance over time because they do many small writes, which can overtax wear-leveling and data combining algorithm. While SSDs can slow over time, Intel's problem was "an edge case," according to Gene Ruth, a senior analyst with the Burton Group.

When it comes to enterprise-class SSDs like Intel's X25-E, most have enough spare memory for efficient background data handling, "allowing higher performance and avoiding the [fragmentation] issue," according to officials from both Intel and STEC.

All flash drives have some bugs, largely due to the NAND flash memory's need for excessive write management, said Jim Handy, an analyst with Objective Analysis in Los Gatos, Calif. "Intel's happened to have surfaced through the application of tests that don't really reflect actual use."

Standard benchmarking metrics

Later in the year SSD fans should get more -- and better -- information about the various drives and SSD technology on the market. Part of the problem so far in evaluating the drives' longevity and performance has been the lack of standards.

The JEDEC plan to publish standards by the end of this year involves two methods to determine the SSD endurance. The first will be targeted at original equipment manufacturers, such as Dell and Lenovo, who will be able to determine the number of erases per block an SSD can sustain. The standard will include predictive life modeling based on various workload classes to confirm, or refute, the stated life expectancy.

A second standard -- targeted at SSD manufacturers -- will be an endurance rating based on an SSD's average performance after use with wear-leveling and write-amplification algorithms. The standard will not be based on pre-erased drives, Intel's Cox said.

"[Drive manufacturers] know the characteristics of their components," he said. "From those numbers, they can determine how many terabytes can be written to that drive or what the drive is capable of [sustaining]. That will be a standardized number you'd see on a manufacturer's box."

Only then are SSD users likely to get the answers to the questions now about how well their drive will perform over its life and how long it will last.

Copyright © 2009 IDG Communications, Inc.

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