Thread: Intel X25-M SSD

The performance problems involving Intel's consumer-grade X25-M SSD were related to its wear-leveling algorithm. To implement wear-leveling, commonly used data has to be moved frequently to different loca¬tions, and that leads to some data fragmentation, said Jim McGregor, chief technology strategist for research firm In-Stat Inc. In Intel's case, reviewers at PC Perspective spent months testing X25-M SSDs using multiple PCs and applications.

The results showed that write speeds dropped from 80MB/sec. when the drives were new, to 30MB/sec. and read speeds dropped from 250MB/sec to 60MB/sec. for some large block writes."We found that a 'used' X25-M will always perform worse than a 'new' one, regardless of any adaptive algorithms that may be at play," PC Perspective wrote. Intel clarified that the drive's performance was related to a bug in the firmware that has since been corrected with an upgrade. PC Perspective retested the drive and found the problem had, indeed, been fixed.



Another factor contributing to SSD performance and endurance degradation is native to all NAND flash memory: write amplification. With NAND flash memory, data is laid down in blocks, just as it is on a hard disk drive. But, unlike a traditional spinning disk, block sizes on an SSD are fixed; even a small 4k chunk of data write can take up to 512k block of space. When any portion of the data on the drive is changed, a block must first be marked for deletion in preparation for accommodating the new data.

The amount of space required for each new write varies and so does write amplification on many consumer SSDs. The latter is anywhere from 15 to 20, which means, for every 1MB of data written, 15 - 20 MB is actually needed.