HomeFiction #1: SSDs with MLC flash cannot be used in enterprise storage
Fact #1: SandForce enables MLC in enterprise storage
SSD OEMs strive to provide products that can tolerate the high duty cycles of enterprise environments. All flash memory sustains a limited number of P/E (program-erase) cycles during their life and for SLC flash memory today it is ~100K. Calculating the life of an SSD is based on a simple formula that uses the total number of cells available for writing and dividing by the number of bytes that can be written in a period of time. That can be translated into years, months or even days depending upon how much data is transferred.
Using a standard SSD controller and commodity MLC memory that only supports 10K P/E cycles, the basic life formula can calculate how long an MLC drive would last in an enterprise environment. The total number of cells available is the product of the capacity of the drive and the number of P/E cycles. The denominator in the equation is the product of the write speed, the duty cycle for what percent of the time the drive will be accessed (reading or writing), the percentage of time the drive is being written (vs. being read), and the “write amplification.” Write amplification is a measurement of additional P/E cycles that must be executed on the flash interface to get data programmed into the flash and in this equation, also takes into account inefficiencies due to wear leveling. For most competitive controllers today the formula below uses a conservative write amplification number of 10 (1GB of data that must be written to the flash causes 10GBs of equivalent P/E cycles), but this number can be even higher than 40 according to industry experts.
Due to the very limited number of program-erase cycles in MLC memory and a high write amplification factor, an SSD built with a standard SSD controller under typical enterprise conditions will only last 92 days! Therefore that MLC flash memory would not be viable in the enterprise without some other solution.
Take that same MLC-based SSD and install a SandForce SSD Processor in place of the standard SSD controller. DuraClass technology adds a feature called DuraWrite to the SSD that reduces the write amplification factor by 20x or even more. Using the same formula and enterprise conditions, that same MLC-based SSD with a SandForce SSD Processor can last 5 years.
