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Re: JFFS2 (not) on CF cards




Hi Charles,
Maybe you can help me with this question I have.  Does JFFS2 resolve or
improve the "squatting" issue you mentioned ?

Thanks,

Steve...





Charles Manning <manningc2@xxxxxxx.com on 03/11/2002 11:23:52
AM

Please respond to manningc2@xxxxxxx.nz

Sent by:  owner-jffs-dev@xxxxxxx.com


To:   Alan Cox <alan@xxxxxxx.org (David
      Woodhouse)
cc:   trevor.pering@xxxxxxx.com

Subject:  Re: JFFS2 (not) on CF cards

On Sat, 09 Mar 2002 05:58, Alan Cox wrote:
> > > How do non-Linux systems handle this (i.e., my camera, windows, mp3
> > > players, etc...) -- I believe they use fat32 or some nonsense, right?
> > > Same problems?
> >
> > yes, yes.
>
> CF cards do wear levelling on card (or are supposed to anyway). Most
> cameras seem to use FAT12/FAT16
>

Well not really.... We've pounded this to death a few times already.

Internally CF does something like what SmartMedia block drivers do; when
they
allocate new blocks for the physical to logical virtualisation layer they
do
this off a pool. ie
When a sector is rewritten, a new block is grabbed from the pool and
unmodified sectors are copied across. The old block is erased released back

into the pool.

This semi-random reuse effects a limited form of wear levelling. This is
not
"counted wear levelling". This kind of wear levelling does not prevent or
correct for seldom-changed files "squatting" on an area of flash and
preventing this area from being levelled.

IMHO CF is a Kleenex technology. While you can use CF in an embedded
system,
it is prone to failure and can thus cause product failure. Rather only use
CF
as a removeable data transfer (as it was designed for).

FAT16 seems to be the most popular. Of course if you need to interchange
data
with cameras, PCs etc, then you don't have too much choice.

-- Charles


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