David Woodhouse David.Woodhouse at mvhi.com
Mon Nov 1 09:45:57 EST 1999

miket at bluemug.com said:
>  Log-structured file systems are also very interesting for Flash-ROMs
> in embedded devices.  Wear leveling is a big concern there, seek time
> is not.  Reconciling proper GC with decent random access times is
> still the trick, though. 

All the solutions we currently have for filesystems on flash present a block 
device rather than a filesystem interface - that is, both FTL and NFTL act as 
an extra translation layer below the actual filesystem, providing 512-byte 
random block access for use by a traditional filesystem. 

It would probably be more efficient to implement a filesystem directly on the 
flash, much like Microsoft's FFS2, except that FFS2 obviously isn't 
POSIX-compliant, and hence isn't very interesting to us, although we do have 
the beginnings of a filesystem driver for it.

As there are patent problems with both FTL and NFTL, it would be extremely 
useful to have a POSIX-compliant filesystem designed specifically for use on 
flash devices. 

I think that there is already such a beast in existence, designed for QNX. It
would be nice to either support this or write a replacement. 

Contact me if you're interested in following this up.

----                                ----                                 ----
David Woodhouse       David.Woodhouse at mvhi.com      Office: (+44) 1223 810302
 Project Leader,    Process Information Systems     Mobile: (+44) 7976 658355
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