After a flash storage device is initially manufactured, the flash controller is first used to format the flash memory. This ensures the device is operating properly, it maps out bad flash memory cells, and it allocates spare cells to be substituted for future failed cells. Some part of the spare cells is also used to hold the firmware which operates the controller and other special features for a particular storage device. A directory structure is created to allow the controller to convert requests for logical sectors into the physical locations on the actual flash memory chips.[1]
When the system or device needs to read data from or write data to the flash memory, it will communicate with the flash memory controller. Simpler devices like SD cards and USB flash drives typically have a small number of flash memory die connected simultaneously. Operations are limited to the speed of the individual flash memory die. In contrast, a high-performance solid-state drive will have more dies organized with parallel communication paths to enable speeds many times greater than that of a single flash die.[citation needed]
Flash memory can withstand a limited number of program-erase cycles. If a particular flash memory block were programmed and erased repeatedly without writing to any other blocks, the one block would wear out before all the other blocks thereby prematurely ending the life of the storage device. For this reason flash controllers use a technique called wear leveling to distribute writes as evenly as possible across all the flash blocks in the SSD. In a perfect scenario this would enable every block to be written to its maximum life so they all fail at the same time.[2]
Usually, flash memory controllers also include the "flash translation layer" (FTL), a layer below the file system that maps host side or file system logical block addresses (LBAs) to the physical address of the flash memory (logical-to-physical mapping). The LBAs refer to sector numbers and to a mapping unit of 512 bytes. All LBAs that represent the logical size visible to and managed by the file system are mapped to a physical location (block ID, page ID and sector ID) of the Flash. As part of the wear leveling and other flash management algorithms (bad block management, read disturb management, safe flash handling etc.), the physical location of an LBA might dynamically change frequently. The mapping units of an FTL can differ so that LBAs are mapped block-, page- or even sub-page-based. Depending on the usage pattern, a finer mapping granularity can significantly reduce the flash wear out and maximize the endurance of a flash based storage media.[3][4][5] The deduplication function to eliminate redundant data and duplicate writes is also added in FTL.[6]
As the FTL metadata takes up its own flash space, it too needs protection in case of power loss. In addition, it is possible for the mapping table to wear out before other parts of the flash memory has, prematurely ending the life of a storage device. This is usually avoided in enterprise devices by allocating an oversized space for spares, although more durable forms of storage like MRAM has been proposed for FTL too.[citation needed]
Once every block of a solid-state storage device has been written one time, the flash controller will need to return to some of the initial blocks which no longer have current data (also called stale blocks). The data in these blocks were replaced with newly written blocks and now they are waiting to be erased so that new data can be written into them. This is a process called garbage collection (GC). All SSDs, CF Cards, and other flash storage devices will include some level of garbage collection. The speed at which a flash controller will do this can vary.[7]
ReferencesEdit
^ ab"Flash Memory Guide" (PDF). kingston.com. Retrieved 7 March 2013.
^Chang, Li-Pin (2007-03-11). "On Efficient Wear Leveling for Large Scale Flash Memory Storage Systems". CiteSeerX10.1.1.103.4903.
^Goodson, Garth; Iyer, Rahul. (PDF). Archived from the original (PDF) on June 23, 2015.
^"Understanding Flash: The Flash Translation Layer". September 17, 2014.
^Heidrich, Susan (February 2015). "New flash management architecture enables MLC for industrial storage" (PDF).
^Chen, Feng; Luo, Tian; Zhang, Xiaodong (2011). CAFTL: a content-aware flash translation layer enhancing the lifespan of flash memory based solid state drives. FAST' 11. p. 6.
^(PDF). OCZ Technology. Archived from the original (PDF) on 2012-05-26. Retrieved 2010-05-31.
October 21, 2023
flash, memory, controller, flash, memory, controller, flash, controller, manages, data, stored, flash, memory, usually, nand, flash, communicates, with, computer, electronic, device, designed, operating, duty, cycle, environments, like, memory, cards, other, s. A flash memory controller or flash controller manages data stored on flash memory usually NAND flash and communicates with a computer or electronic device Flash memory controllers can be designed for operating in low duty cycle environments like memory cards or other similar media for use in PDAs mobile phones etc USB flash drives use flash memory controllers designed to communicate with personal computers through the USB port at a low duty cycle Flash controllers can also be designed for higher duty cycle environments like solid state drives SSD used as data storage for laptop computer systems up to mission critical enterprise storage arrays 1 Lexar USB stick 8 GB Silicon Motion SM3253L USB 2 0 single channel flash controller Contents 1 Initial setup 2 Reading writing and erasing 3 Wear leveling and block picking 4 Flash translation layer FTL and mapping 5 Garbage collection 6 ReferencesInitial setup EditAfter a flash storage device is initially manufactured the flash controller is first used to format the flash memory This ensures the device is operating properly it maps out bad flash memory cells and it allocates spare cells to be substituted for future failed cells Some part of the spare cells is also used to hold the firmware which operates the controller and other special features for a particular storage device A directory structure is created to allow the controller to convert requests for logical sectors into the physical locations on the actual flash memory chips 1 Reading writing and erasing EditMain article Flash memory Principles of operation When the system or device needs to read data from or write data to the flash memory it will communicate with the flash memory controller Simpler devices like SD cards and USB flash drives typically have a small number of flash memory die connected simultaneously Operations are limited to the speed of the individual flash memory die In contrast a high performance solid state drive will have more dies organized with parallel communication paths to enable speeds many times greater than that of a single flash die citation needed Wear leveling and block picking EditMain article Wear leveling Flash memory can withstand a limited number of program erase cycles If a particular flash memory block were programmed and erased repeatedly without writing to any other blocks the one block would wear out before all the other blocks thereby prematurely ending the life of the storage device For this reason flash controllers use a technique called wear leveling to distribute writes as evenly as possible across all the flash blocks in the SSD In a perfect scenario this would enable every block to be written to its maximum life so they all fail at the same time 2 Flash translation layer FTL and mapping EditMain article Flash file system Usually flash memory controllers also include the flash translation layer FTL a layer below the file system that maps host side or file system logical block addresses LBAs to the physical address of the flash memory logical to physical mapping The LBAs refer to sector numbers and to a mapping unit of 512 bytes All LBAs that represent the logical size visible to and managed by the file system are mapped to a physical location block ID page ID and sector ID of the Flash As part of the wear leveling and other flash management algorithms bad block management read disturb management safe flash handling etc the physical location of an LBA might dynamically change frequently The mapping units of an FTL can differ so that LBAs are mapped block page or even sub page based Depending on the usage pattern a finer mapping granularity can significantly reduce the flash wear out and maximize the endurance of a flash based storage media 3 4 5 The deduplication function to eliminate redundant data and duplicate writes is also added in FTL 6 As the FTL metadata takes up its own flash space it too needs protection in case of power loss In addition it is possible for the mapping table to wear out before other parts of the flash memory has prematurely ending the life of a storage device This is usually avoided in enterprise devices by allocating an oversized space for spares although more durable forms of storage like MRAM has been proposed for FTL too citation needed Garbage collection EditMain article Garbage collection SSD Once every block of a solid state storage device has been written one time the flash controller will need to return to some of the initial blocks which no longer have current data also called stale blocks The data in these blocks were replaced with newly written blocks and now they are waiting to be erased so that new data can be written into them This is a process called garbage collection GC All SSDs CF Cards and other flash storage devices will include some level of garbage collection The speed at which a flash controller will do this can vary 7 References Edit a b Flash Memory Guide PDF kingston com Retrieved 7 March 2013 Chang Li Pin 2007 03 11 On Efficient Wear Leveling for Large Scale Flash Memory Storage Systems CiteSeerX 10 1 1 103 4903 Goodson Garth Iyer Rahul Design Tradeoffs in a Flash Translation Layer PDF Archived from the original PDF on June 23 2015 Understanding Flash The Flash Translation Layer September 17 2014 Heidrich Susan February 2015 New flash management architecture enables MLC for industrial storage PDF Chen Feng Luo Tian Zhang Xiaodong 2011 CAFTL a content aware flash translation layer enhancing the lifespan of flash memory based solid state drives FAST 11 p 6 SSDs Write Amplification TRIM and GC PDF OCZ Technology Archived from the original PDF on 2012 05 26 Retrieved 2010 05 31 Retrieved from https en wikipedia org w index php title Flash memory controller amp oldid 1168188778, wikipedia, wiki, book, books, library,
