Flash file systems use non-volatile flash memory to store data in blocks that must be completely erased before being written. Wear leveling balances frequently used parts of the memory with less used parts. Data is found using maps stored within flash devices, and data retention depends on the number of write and erase cycles and operating temperature.
A flash file system consists of a type of electronically erasable programmable read-only memory (EEPROM) called flash memory. It is one of the most popular methods of storing data and is non-volatile, which means it retains information even when there is no power. Found in data center servers as well as cell phones and handheld computers, a flash file system is organized into blocks of data, each of which must be completely erased before being written. The standard erase block holds about 128 kilobytes of data, and some blocks can store up to 2,048 kilobytes.
Memory in a flash file system cannot be held indefinitely. After a certain number of write and erase cycles, the data becomes corrupted and sections of memory can no longer be used. Wear leveling is used to create a balance between parts of the flash that are used frequently and others that are not. The dynamic wear leveling process can lead to large blocks of a disk with data that is rarely altered, causing frequent changes in other areas. A more static strategy moves data to more used places to make balancing more efficient.
In a flash file system, data is found using a method of mapping data blocks and sectors. These data structure maps are stored within flash devices and update as changes are made to the data using special assigned identities for each block. Sectors and blocks map automatically when a rewrite cycle occurs in random access memory, but in a flash system, an indirect map helps link sectors with blocks. Data can be found faster with a direct map that is stored in the flash transaction layer, a kind of interface section that contains information about the data assigned to the various blocks and erasure units.
Data retention is often cited as an advantage for the flash file system. The duration of data security depends on the operating temperature and the number of write and erase cycles a storage device can undergo before system performance degrades. Many flash systems are rated to last 20 years and tolerate 1,000 to 1,000,000 erase cycles. The more frequently data is written and erased, and the hotter the temperatures, the shorter the overall life expectancy of the retained data and memory system.
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