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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.
Because flash memory must be erased before it can be rewritten, with much coarser granularity of the erase operation when compared to the write operation,[a] the process to perform these operations results in moving (or rewriting) user data and metadata more than once. 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. 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. This multiplying effect increases the number of writes required over the life of the SSD, which shortens the time it can operate reliably. The increased writes also consume bandwidth to the flash memory, which reduces write performance to the SSD.[1][3] 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.
Intel and SiliconSystems (acquired by Western Digital in 2009) used the term write amplification in their papers and publications in 2008.[4] WA is typically measured by the ratio of writes committed to the flash memory to the writes coming from the host system. Without compression, WA cannot drop below one. Using compression, SandForce has claimed to achieve a write amplification of 0.5,[5] with best-case values as low as 0.14 in the SF-2281 controller.[6]
- ^ a b Hu, X.-Y.; E. Eleftheriou; R. Haas; I. Iliadis; R. Pletka (2009). Write Amplification Analysis in Flash-Based Solid State Drives. IBM. CiteSeerX 10.1.1.154.8668.
- ^ Thatcher, Jonathan (2009-08-18). "NAND Flash Solid State Storage Performance and Capability – an In-depth Look" (PDF). SNIA. Retrieved 2012-08-28.
- ^ Smith, Kent (2009-08-17). "Benchmarking SSDs: The Devil is in the Preconditioning Details" (PDF). SandForce. Retrieved 2016-11-10.
- ^ Lucchesi, Ray (September 2008). "SSD Flash drives enter the enterprise" (PDF). Silverton Consulting. Retrieved 2010-06-18.
- ^ Shimpi, Anand Lal (2009-12-31). "OCZ's Vertex 2 Pro Preview: The Fastest MLC SSD We've Ever Tested". AnandTech. Retrieved 2011-06-16.
- ^ Ku, Andrew (6 February 2012). "Intel SSD 520 Review: SandForce's Technology: Very Low Write Amplification". TomsHardware. Retrieved 10 February 2012.
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