Two Methods for Measuring SSD Lifespans

Solid State Drives (SSDs) are very quickly becoming a very popular alternative to traditional, platter-based hard drives. Not only can SSDs read and write data quicker overall, but since they have no moving parts, they can withstand a lot more abuse than traditional hard drives. SSDs are still relatively expensive and available storage capacity limits still pale in comparison to today's traditional hard drive options; but as the technology matures, prices are steadily coming down, and storage capacities are going up. If not for one significant potential flaw, SSDs might appear to be the perfect storage medium.

That one potential flaw is in some sense, one of a perception. Because the actual lifespan of NAND flash-based SSDs is such an unknown quotient, many are reluctant to make the switch to SSDs--especially for mission-critical applications, such as file and data-servers, where the drives' potentially fast transactions would seem ideal. Inherent in NAND flash technology is the fact that "there is a limitation in the number of write/erase cycles (endurance)" that each NAND Flash cell is capable. Because of this finite nature of the NAND Flash cell, SSDs can be received as potentially unreliable for long-term usage.

 Credit: SiliconSystems

Aliso Viejo, California-based, SiliconSystems argues that if you can know how long an SSD will last and therefore "eliminate this guesswork," it will make SSDs more reliable, because you'll know how long each SSD should last for. So, SiliconSystems has created two tools, which it claims are "the first to develop a comprehensive method to measure solid-state drive (SSD) useable life."

The first tool is LifeEST (which stands for life estimation) and it is actually an endurance metric, proposed by SiliconSystems, which is "independent of capacity and usage model." SiliconSystems's white paper, "NAND Evolution And Its Effects On Solid-State Drive (SSD) Useable Life" (PDF), explains LifeEST as:

"It specifically measures performance and storage management algorithms implemented in the SSD. Using NAND components with a higher endurance rating will increase LifeEst. Decreasing the write amplification will also have a positive impact on useful life, as will slowing down the SSD."

The paper explains that the LifeEST parameter "yields a value of 'write years per gigabyte.' Multiplying this value by the capacity in gigabytes and dividing by the write duty cycle yields a lifetime estimate in years."

  Credit: SiliconSystems

SiliconSystems concedes that the LifeEST parameter is still such a theoretical calculation, and that what is also needed is a methodology that can generate "real world results." So the second tool that SiliconSystems has is its own "patent-pending SiSMART technology," which monitors "the exact wear of the NAND flash and report[s] that data back to the host." This is what SiliconSystems calls "endurance monitoring" and the technology is actually built-in to all of the hard drives that SiliconSystems manufacturers. The SiliconSystems white paper explains:

"Using this methodology, the SiliconDrive will yield real-world, application-specific usage information without requiring software development on the part of the OEM. Simply load the SiliconDrive into the application and run it for an hour, a day, a week, a month, or any time that makes sense. SiSMART reports the usage percentage during that time. Upon test completion, simply take the SiliconDrive out of the test system and plug it in to any Windows or Linux based computer and run the SiliconSystems SiliconDrive Utility to measure the usage at the NAND media level."

   Credit: SiliconSystems

SiliconSystems argues that knowing the theoretical life of an SSD combined with having real-world endurance data should give you a very good indication of what kind of lifespan to expect from an SSD. It is unknown at this early point, however, if other SSD manufacturers will adopt SiliconSystems' tools or other similar tools that can accurately gauge the lifespan of an SSD.