Re: [ECOS] FAT on NOR/ NAND flash

[Ross Younger <wry at ecoscentric dot com>]

viren.dobariya wrote:
>    I am trying to port FAT on NOR flash of EA2468 board.

Running FAT on a raw flash device is not a good idea. I would suggest 
that you use a different filesystem more suited to flash memory parts - 
jffs2 and yaffs come to mind - or, if you really insist on using FAT, 
implement a flash translation layer including wear levelling.


FAT was designed for media with small (often 512 bytes) sectors which 
are individually rewritable (floppy drives, hard drives); NOR flash 
devices can only be erased at the block level (64k or more). You'll have 
an awful lot of trouble making it work properly. Because of this it is 
also quite dangerous: the length of time taken to erase and reprogram a 
whole block is much longer than it takes to write a sector to magnetic 
media, leaving you very vulnerable to power supply issues.

Furthermore, the filesystem stores its file allocation table at fixed 
sector locations. This leads to those regions of your flash device 
experiencing a disproportionate amount of use; they will likely wear out 
quickly, rendering your filesystem useless.


Ross

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