Re: Compact Flash Question

[Helge Hafting <helge.hafting@aitel.hist.no>]

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