Flash Filesystems

[Eugeny S. Mints]

Hi, all!


On Wed, 16 Jul 2003 20:19:41 -0500, Chris Caudle <chris at chriscaudle.org> 
wrote:

> On Wed July 16 2003 6:03 pm, Chris Johns wrote:
>> We have the DOSFS code working with compact flash cards.
>
> Watch out for sector lifetime when using DOSFS.  The FAT normally goes to 
> the same sector, so if you change files a lot (extend, add, delete, etc.) 
> you can change the FAT so many times that it wears out.  Usually only a 
> problem if you have files into the thousands, but something to consider.
> Typical write lifespan of Flash would be on the order of 100 000, but the 
> FAT could be updated multiple times for each file.  One person reported 
> problems with flash disk failure after copying on the order of 25 000 
> files when using FAT file system.

General solution assumed is the following. You need to configure libblock 
in a such way which is the most suitable for you own unique DOSFS 
utilization case. Somebody may need speed up, somebody may need robustness.

Currently libblock configuration involves configuration of cache buffers 
number and flush task priority. In general it also possible to configure 
cache algorithms employed but for now you need to modify libblock source 
code for this purpose(unfortunately, libblock version which allows to 
configure cache algorithms even "on-the-fly" hasn't finished yet and 
postponed:(

But even for now I think it is possible to avoid(or at least to improve) 
behaviour you described above by configuration of appropriate cache buffers 
number and by coordination of LRU algorithm currently employed in libblock 
with user access to files under DOSFS. I mean organization of user access 
in a such way that the cache buffer which contains FAT sector will be not 
overloaded by other data as long as possible. For this, it is also 
important how your files are spaned across the hard disk.( I mean 
fragmentation)

Victor, any comments?

Regards,
			Eugeny