Algorithms and data structures for flash memories

Abstract

Flash memory is a type of electrically-erasable programmable read-only memory (EEPROM). Because flash memories are nonvolatile and relatively dense, they are now used to store files and other persistent objects in handheld computers, mobile phones, digital cameras, portable music players, and many other computer systems in which magnetic disks are inappropriate. Flash, like earlier EEPROM devices, suffers from two limitations. First, bits can only be cleared by erasing a large block of memory. Second, each block can only sustain a limited number of erasures, after which it can no longer reliably store data. Due to these limitations, sophisticated data structures and algorithms are required to effectively use flash memories. These algorithms and data structures support efficient not-in-place updates of data, reduce the number of erasures, and level the wear of the blocks in the device. This survey presents these algorithms and data structures, many of which have only been described in patents until now.

Enhancing Endurance of Huge-Capacity Flash Storage Systems by Selectively Replacing Data Blocks

“…If block B is the updated one, search new block B (step 6-8). After that, pick an empty block (step 9) and compare its erase cycles with both n A and n B (step [10][11][12][13][14][15][16][17]. Note that searching new P A or P B costs much time for huge-capacity systems, but as the frequency of updating block A or block B is very low and static wear leveling is not time critical when dynamic wear leveling exists, the time cost is acceptable.…”

Flash-Aware Buffer Management for Database Systems

“…Logical block addresses are mapped by the FTL to varying locations on the physical medium. This mapping is required due to the intrinsic limitations of flash memory (Woodhouse, 2001;Gal & Toledo, 2005). The FTL implementation is device-related and supplied by the disk manufacturer.…”

An Empirical Study of FTL Performance in Conjunction with File System Pursuing Data Integrity

“…Flash storage normally adopts an FTL to efficiently manage the underlying Flash memory. As the efficiency of FTL dominates the performance of Flash storage, issues related to improving FTL performance have been the focus of much research [5], [8], [9]. In addition to the I/O performance enhancement of Flash storage, it is important to assure the data integrity stored in Flash memory against system crashes such as sudden power failure or unexpected removal of the Flash storage.…”