Debunking Misconceptions in SSD Longevity

Aside from flash memory prices, the write endurance limitation of flash memory is probably one of the remaining impediments to the widespread application of non-volatile solid-state storage in the enterprise. Flash SSD critics have long harped on this apparent weakness that remains a thorn on the side of SSD manufacturers despite the development of advanced error correcting codes and wear leveling techniques utilized in their products. In a recent article on write endurance published in STORAGEsearch.com, editor Zsolt Kerekes provided theoretical computations on the longevity of flash SSDs deployed in enterprise server applications. His test SSD had the following specifications: total capacity of 64GB, sustained write speed of 80MBps and a write endurance rating of 2 million cycles. By assuming that data is written in big blocks and there is perfect implementation of wear leveling techniques, Kerekes estimates disk endurance at 1.6 billion seconds, which translates to 50.74 years. Kerekes noted that for real-life applications, the aforementioned model should take into account the ratio and interaction of write block size, cache operation and internal flash block size. I ve assumed perfect cache operation - and sequential writes - because otherwise you don t get the maximum write speed. Conversely if you aren t writing at the maximum speed - then the disk will last longer. Other factors which would tend to make the disk last longer are that in most commercial server applications such as databases - the ratio of reads to writes is higher than 5 to 1. And as there is no wear-out or endurance limit on read operations - the implication is to increase the operating life by the read to write ratio. A few years back, BiTMICRO published an article that arrived at a different conclusion with regard to flash SSD endurance in database applications. Although the write endurance rating for BiTMICRO s computations is smaller (1 million cycles), endurance ratings are much higher as a result of wear leveling methods, proprietary RS ECC and other techniques designed to prolong the life of E-Disk SSDs. Assuming a much smaller endurance rating of 100,000 cycles (typical rating quoted by NAND flash vendors), a bigger volume of writes per day at 3.4TB and no caching nor wear leveling implementations, a 160GB SSD is projected to last up to 12.9 years, which is definitely longer than the average life cycle of most IT storage devices and equipment. BiTMICRO Networks value proposition is plain and simple: a proven and tested platform that delivers superior storage performance. E-Disk SSDs has been deployed countless times in rugged data recording applications where data is constantly streamed and recorded onto the disks on a 24 hours by 7 days/week basis. Most SSD manufacturers are marketing their products as silver bullet solutions to performance and reliability issues in storage. These makers have even quoted higher write endurance ratings than those provided by manufacturers of their flash memory components. Based on the preceding computations (showcasing very conservative estimates) and the ever-increasing capacities of SSD products, we can safely conclude that fears about the endurance limitations of SSDs are rightfully fading away.



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