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Analytical View Of Garbage Collection In Solid State Media File Systems

Analytical View of Garbage Collection in Solid State Media File Systems

Nilay Khandelwal and Veni Taneja

(Thesis written under the course Operating Systems)
Department of Computer Science & Engineering
Jaypee Institute of Information Technology, India

nilay.khandelwal@gmail.com, venitaneja@gmail.com


1.0 Overview
Solid State media's such as flash memory are non-volatile computer memory that can be electrically erased and reprogrammed. These are specific types of EEPROM's that are erased and programmed in large blocks.
Flash memory is non-volatile, which means that it does not need power to maintain the information stored in the chip. In addition, flash memory offers fast read access times and better kinetic shock resistance than hard disks (Table 1).
Though flash memory has many advantages, its special hardware characteristics impose design challenges on storage systems.
Media Access Time
Read (512B) Write (512B) Erase
DRAM 2.56µs 2.56µs -
NOR Flash 14.4µs 3.53ms 1.2s (128kB)
NAND Flash 135.9µs 226µs 2-3ms (16kB)
Disk 12.4ms 12.4ms -

Table 1. Characteristics of different storage media. (NOR Flash: Intel 28F128JF3A-150, NAND Flash: K9F5608U0M)

1.1 Architecture
1.1.1 Partitions
Flash memory is divided into one or many sections of memory called partitions. A multi-partition architecture allows system processor to multi-task the I/O operations with the flash memory. While the processor can read from one partition, it can write/erase in another.

Figure 1. Partitions, Blocks and Pages
1.1.2 Blocks
In addition to partitions, flash memory is further divided into sections of memory called blocks (Figure 1). Flash memory devices in which all blocks are of the same size are symmetrically-blocked, while devices which are asymmetrically-blocked generally have several blocks that are significantly smaller than main array of flash blocks. Small blocks are typically used for storing small data or boot code. Block sizes vary 64kB to 256kB....