This is often referred to as the maximum number of program/erase cycles (P/E cycles) it can sustain over the life of the flash memory. įlash memory can be programmed and erased only a limited number of times. The data in the former location is no longer valid, and will need to be erased before that location can be written to again.
#Ata secure erase command update#
When new data comes in replacing older data already written, the SSD controller will write the new data in a new location and update the logical mapping to point to the new physical location. The SSD controller on the SSD, which manages the flash memory and interfaces with the host system, uses a logical-to-physical mapping system known as logical block addressing (LBA) that is part of the flash translation layer (FTL). When data is first written to an SSD, the cells all start in an erased state so data can be written directly using pages at a time (often 4–8 kilobytes (KB) in size). ĭue to the nature of flash memory's operation, data cannot be directly overwritten as it can in a hard disk drive. NAND flash memory writes data in 4 KiB pages and erases data in 256 KiB blocks. Using compression, SandForce has claimed to achieve a write amplification of 0.5, with best-case values as low as 0.14 in the SF-2281 controller. Without compression, WA cannot drop below one. WA is typically measured by the ratio of writes committed to the flash memory to the writes coming from the host system. Intel and SiliconSystems (acquired by Western Digital in 2009) used the term write amplification in their papers and publications as early as 2008. Many factors will affect the WA of an SSD some can be controlled by the user and some are a direct result of the data written to and usage of the SSD. The increased writes also consume bandwidth to the flash memory, which reduces random write performance to the SSD. This multiplying effect increases the number of writes required over the life of the SSD, which shortens the time it can operate reliably. Due to the way flash works, much larger portions of flash must be erased and rewritten than actually required by the amount of new data. Thus, rewriting some data requires an already-used-portion of flash to be read, updated, and written to a new location, together with initially erasing the new location if it was previously used at some point in time. Write amplification ( WA) is an undesirable phenomenon associated with flash memory and solid-state drives (SSDs) where the actual amount of information physically written to the storage media is a multiple of the logical amount intended to be written.īecause flash memory must be erased before it can be rewritten, with much coarser granularity of the erase operation when compared to the write operation, the process to perform these operations results in moving (or rewriting) user data and metadata more than once. An SSD experiences write amplification as a result of garbage collection and wear leveling, thereby increasing writes on the drive and reducing its life.
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