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SubjectRe: Compact Flash Question
Tomasz Chmielewski wrote:
>
> How does it work, then?
> How can it do wear levelling over the whole CF if some (or most) area
> of CF is already used by our precious data/metadata?
> It would have to know the areas where no data is stored, but it
> contradicts the CF <-> filesystem separation.
It don't necessarily need to know. It can swap two used blocks, one
often-used and one
rarely-used. That way the rarely-used block is rewriten over the
previously busy
block, and the busy block is moved to the rarely used area that isn't worn.
This implies an extra write whenever a busy block is moved. Don't know if
anybody do this, but the technique is simple enough.

CF-filesystem separation is necessary, for they can't know in advance what
filesystem or partitioning scheme will be used. (I have ext3 on CF, for
example...)

Helge Hafting




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