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
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
Axiom (Cambridge) Ltd., Swaffham Bulbeck, Cambridge, CB5 0NA, UK.
finger dwmw2 at ferret.lmh.ox.ac.uk for PGP key.
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