RAM 6.0 BUX II Series Guía de usuario descargar pdf (Pagina 31)

8. Flash Devices and Flash File System Support

known as the cycling limit, depends on the specific flash technology, but it ranges

from a hundred thousand to a million times per block.

Optimization Methods

As mentioned, flash memory is not an infinitely reusable storage medium. The

number of erase cycles per erase unit of flash memory is large but limited.

Eventually, flash degrades to a read-only state. To delay this as long as possible,

TrueFFS uses a garbage collection algorithm that works in conjunction with a

technique called wear-leveling.

Wear-Leveling

One way to alleviate over-programming is to balance usage over the entire

medium, so that the flash is evenly worn and no one part is over-used. This

technique is known as wear-leveling and it can extend the lifetime of the flash

significantly. To implement wear-leveling, TrueFFS uses a block-to-flash

translation system that is based on a dynamically maintained map. This map is

adjusted as blocks are modified, moved, or garbage collected.

Static File Locking

By remapping modified blocks to new flash memory coordinates, a certain degree

of wear-leveling occurs. However, some of the data stored in flash may be

essentially static, which means that if wear-leveling only occurs during

modifications, the areas of flash that store static data are not cycled at all. This

situation, known as static file locking, exacerbates the wear on other areas of flash,

which must be recycled more frequently as a consequence. If not countered, this

situation can significantly lower the flash medium’s life-expectancy.

TrueFFS overcomes static file locking by forcing transfers of static areas. Because

the block-to-flash map is dynamic, TrueFFS can manage these wear-leveling

transfers in a way that is invisible to the file system.

Algorithm

Implementing absolute wear-leveling can have a negative impact on performance

because of the many required data moves. To avoid performance degradation,

TrueFFS implements a wear-leveling algorithm that is not quite absolute. This

algorithm provides an approximately equal number of erase cycles per unit. Over

time, you can expect the same number of erase cycles per erase unit without a

1. This number is statistical in nature and should not be taken as an exact figure.

1 2 ... 26 27 28 29 30 31 32 33 34 35 36

Sin comentarios

RAM 6.0 BUX II Series Guía de usuario Pagina 31