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SSD MTBF Rating - Meaningless in Flash Drive Reliability Estimate

Posted by Biraj Jamalayam on Wednesday, 05 Feb 2014

Many Flash Drive manufacturers provide a Mean Time Between Failure (MTBF) rating as an estimate of an SSD life expectancy. Typically this rating is >2,000,000 hours for an SLC (Single Level Cell) NAND based SSD or >1,000,000 hours for an MLC (Multi-Level Cell) based SSD. While at a first glance 1 Million hours (114 years) of life expectancy seems like a huge overkill for a typical application, in reality an MTBF number is not representative of the realistic expected usage of the Flash SSD.

MTBF is a theoretical formula based on the sum of the Mean Time To Failure (MTTF) rates of the individual components used in a specific SSD design.

Formula to calculate MTBF for a Flash SSD, Card or Module

This formula considers each and every component to be equally responsible for the overall failure of the system. Therefore, while a single component, such as Flash memory, could have a poor MTTF rating, the selection of higher rated ancillary components dramatically skews the drive reliability. Even the manufacturers of the electronic components note the inherent uncertainty in the usage of MTTF and MTBF in estimating reliability and life expectancy of the end product.

In addition, the MTBF rating doesn’t take into consideration the real application drive usage model, such as read VS. write utilization, small vs. large size data writes, write acceleration and efficiency, etc. Other methods of SSD life time estimate have been developed to be much better predictors of drive life expectancy than the MTBF rating.

Please contact Fortasa to discuss reliability requirements for your Solid State Storage needs.