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Flash memory possesses a finite erase/program cycle capability.
TLC NAND datasheets guarantee up to 800 P/E cycles.
MLC NAND datasheets guarantee at least 3,000 such cycles per physical block.
SLC NAND datasheets guarantee between 30,000-100,000 P/E cycles.
Field deployments indicate that each SLC NAND block rated at 100k PEC can be typically erased and programmed 200,000 to 1,000,000 times (or even more) before the end of life. The newest TLC/QLC NAND generations do not seem to have, typically, such a margin of safety.
NAND wear out is manifested by Flash controller inability to erase,
or program, the cell within the allocated time.
For many years Flash storage manufacturers tried to convince their customers that write endurance is a problem of the past. Effectively, wear-leveling combined with EDC /ECC techniques made Flash based storage devices bullet proof for consumer, and most industrial and defense storage products.
These devices have operated at relatively low transfer rates. The majority of applications were read intensive. In addition, the industrial and defense customers typically controlled system design and worked with Flash SSD manufacturers to ensure that write endurance is not a limiting factor.
These applications did not push Flash write endurance to its limits. It is quite comforting to realize that SLC NANAD based Flash SSD when overwritten once per day, would reach write endurance limit in about 250 years.
Today, Flash SSD's achieved sufficient capacity and performance to be deployed in main stream notebook, server, data recorders and similar performance intensive applications. The Flash memory transformation from niche to core storage technology is in the making.
These new applications will define the new limits for Flash SSD's.
Today's Flash SSDs support sustained writing speed of up to 100 plus MB/s. A 64GB drive would be overwritten 135 times per day. The drive will reach its write endurance within 2 years of such operations.
The MS Windows uses various log files. 4kB of data is written to the log file every second. The majority of high end Flash SSD's use dynamic wear leveling. With no additional steps, the write endurance limits could be reached within months of operations in such system.
The flash memory has seriously challenged the HDD supremacy as primary computer storage in virtually all applications and the technology already proved itself in most consumer or enterprise deployments where product lifespan is rather short. Memkor believes however that in the Military and Industrial applications such as data recorders and fast continues storage, industrial temperatures do not allow substantiating the theoretical so far "no problem" claim.
The Flash SSD industry has to continue openly discussing and monitoring the Flash SSD write endurance performance before it disappears from the specifications.
It is also our obligation to ensure that factors influencing write endurance are known.
Flash Self Monitoring, Analysis and Reporting Technology (SMART) can be used to monitor Flash SSD NAND usage status. Monitoring the number of available spare blocks and the most stressed portion of memory provides an excellent view on the NAND health. The depletion of spare block pool may indicate that NAND is approaching end of life and needs to be replaced.
The SMART technology is available on all Memkor SATA and PATA products including Industrial Compact Flash drives.
The 3.5" form factor PATA Flash SSD's are also equipped with an LED indicators indicating Flash health.
Let's first review basic Flash memory organization and NAND operations. It helps to understand the relationship between application and Flash SSD life expectancy prediction.