A solid-state drive (SSD) is a solid-state storage device that uses integrated circuit assemblies as memory to store data persistently. SSD technology primarily uses. På denne side har du mulighed for at spørge ind til alt omkring SSD Diske. Det kan være alt - også hvilken en der passer til din computer. Spørg løs! Write amplification (WA) is an undesirable phenomenon associated with flash memory and solid-state drives (SSDs) where the actual amount of information physically. · Windows 7 Forums is the largest help and support community, providing friendly help and advice for Microsoft Windows 7 Computers such as Dell, HP, Acer, Asus or a. Write amplification - Wikipedia. An SSD experiences write amplification as a result of garbage collection and wear leveling, thereby increasing writes on the drive and reducing its life.[1]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 at some point in time; 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 reliably operate. The increased writes also consume bandwidth to the flash memory which mainly reduces random write performance to the SSD.[1][3] Many factors will affect the write amplification 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 Silicon. Systems (acquired by Western Digital in 2. Write amplification is typically measured by the ratio of writes committed to the flash memory to the writes coming from the host system. Without compression, write amplification cannot drop below one. Using compression, Sand. Force has claimed to achieve a typical write amplification of 0. SF- 2. 28. 1 controller.[6]Basic SSD operation[edit]NAND flash memory writes data in 4 Ki. B pages and erases data in 2. Ki. B blocks.[2]Due to the nature of flash memory's operation, data cannot be directly overwritten as it can in a hard disk drive. 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)[update] in size). 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) and that is part of the flash translation layer (FTL).[7] 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 data in the old location is no longer valid, and will need to be erased before the location can be written again.[1][8]Flash memory can be programmed and erased only a limited number of times. 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. Single- level cell (SLC) flash, designed for higher performance and longer endurance, can typically operate between 5. As of 2. 01. 1[update], multi- level cell (MLC) flash is designed for lower cost applications and has a greatly reduced cycle count of typically between 3,0. Since 2. 01. 3, triple- level cell (TLC) flash has been available, with cycle counts dropping to 1,0. P/E) cycles. A lower write amplification is more desirable, as it corresponds to a reduced number of P/E cycles on the flash memory and thereby to an increased SSD life.[1]Calculating the value[edit]Write amplification was always present in SSDs before the term was defined, but it was in 2. Intel[4][9] and Silicon. Systems started using the term in their papers and publications.[1. All SSDs have a write amplification value and it is based on both what is currently being written and what was previously written to the SSD. In order to accurately measure the value for a specific SSD, the selected test should be run for enough time to ensure the drive has reached a steady state condition.[3]A simple formula to calculate the write amplification of an SSD is: [1][1. Factors affecting the value[edit]Many factors affect the write amplification of an SSD. The table below lists the primary factors and how they affect the write amplification. For factors that are variable, the table notes if it has a direct relationship or an inverse relationship. For example, as the amount of over- provisioning increases, the write amplification decreases (inverse relationship). If the factor is a toggle (enabled or disabled) function then it has either a positive or negative relationship.[1][7][1. Write amplification factors. Factor. Description. Type. Relationship*Garbage collection. The efficiency of the algorithm used to pick the next best block to erase and rewrite. Variable. Inverse (good)Over- provisioning. The percentage of physical capacity which is allocated to the SSD controller. Variable. Inverse (good)TRIM command for SATA or UNMAP for SCSIThese commands must be sent by the operating system (OS) which tells the storage device which sectors contain invalid data. SSDs consuming these commands can then reclaim the pages containing these sectors as free space when the blocks containing these pages are erased instead of copying the invalid data to clean pages. Toggle. Positive (good)Free user space. The percentage of the user capacity free of actual user data; requires TRIM, otherwise the SSD gains no benefit from any free user capacity. Variable. Inverse (good)Secure erase. Erases all user data and related metadata which resets the SSD to the initial out- of- box performance (until garbage collection resumes)Toggle. Positive (good)Wear leveling. The efficiency of the algorithm that ensures every block is written an equal number of times to all other blocks as evenly as possible. Variable. Direct (bad)Separating static and dynamic data. Grouping data based on how often it tends to change. Toggle. Positive (good)Sequential writes. In theory, sequential writes have a write amplification of 1, but other factors will still affect the value. Toggle. Positive (good)Random writes. Writing to non- sequential LBAs will have the greatest impact on write amplification. Toggle. Negative (bad)Data compression which includes data deduplication. Write amplification goes down and SSD speed goes up when data compression and deduplication eliminates more redundant data. Variable. Inverse (good)Using MLC NAND in SLC mode. This writes data at a rate of one bit per cell instead of the designed number of bits per cell (normally two bits per cell) to speed up reads and writes. If capacity limits of the NAND in SLC mode are approached, the SSD must rewrite the oldest data written in SLC mode into MLC or TLC mode to allow space in the SLC mode NAND to be erased in order to accept more data. However, this approach can reduce wear by keeping frequently- changed pages in SLC mode to avoid programming these changes in MLC or TLC mode, because writing in MLC or TLC mode does more damage to the flash than writing in SLC mode. Therefore, this approach drives up write amplification but could reduce wear when writing patterns target frequently- written pages. However, sequential- and random- write patterns will aggravate the damage because there are no or few frequently- written pages that could be contained in the SLC area, forcing old data to need to be constantly be rewritten to MLC or TLC from the SLC area. Toggle. Negative (bad)*Relationship definitions. Type. Relationship modified. Description. Variable. Direct. As the factor increases the WA increases. Inverse. As the factor increases the WA decreases. Toggle. Positive. When the factor is present the WA decreases. Negative. When the factor is present the WA increases. Garbage collection[edit]. Pages are written into blocks until they become full. Then, the pages with current data are moved to a new block and the old block is erased.[2]Data is written to the flash memory in units called pages (made up of multiple cells). However, the memory can be erased only in larger units called blocks (made up of multiple pages).[2] If the data in some of the pages of the block are no longer needed (also called stale pages), only the pages with good data in that block are read and rewritten into another previously erased empty block.[3] Then the free pages left by not moving the stale data are available for new data.
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