Doubts about File Systems on FIASCO on ARM (Cortex-A15)

Martin Schröder martin.schroeder at openlimit.com
Fri Jun 20 12:02:59 CEST 2014


Am 19.06.2014 18:06, schrieb Jorge Ventura:
> This is a good direction. I forgot that, in reality we need two drivers,
> one for a block device and another one for the filesystem itself.
>

The two drivers are not sufficient if the underlying hardware is some 
sort of bare flash devices (NOR, NAND) and you use a traditional file 
system. The number of erase cycles of an individual block is limited. So 
writes of frequently written blocks (directory, file allocation table) 
need to be evenly spread over the device to avoid a premature death of 
vital blocks. This is the so called wear levelling which is an 
additional driver in between the block device driver and the file system 
driver. Or you use a file systems which incorporates wear levelling 
(JFFS2, UBIFS).

The two drivers are sufficient only if the underlying hardware is an 
intelligent device like a hard disk, SSD, SD card or USB Stick. Such 
devices have their own controller performing wear levelling itself.


Martin



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