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Re: FAT on NOR/ NAND flash


On 05/26/2010 04:17 AM, viren.dobariya wrote:
hi, Ross
Thanks for your quick response.
But now at primary stage, I want to check that it will work or not.
So plz tell me basic requirement to port FAT on nor flash.

Did you even read his reply? Everything that you are asking for has already been provided (short of doing all the work for you).

Use a file system suited for FLASH; leave FAT for other devices...


On Wed, 2010-05-26 at 10:58 +0100, Ross Younger wrote:
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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