[linux-mm-cc] [OFFTOPIC] SD wear-levelling (was: (no subject))

[John Kielkopf]

On Wed, Sep 1, 2010 at 2:36 AM, Stefan  Monnier <monnier at iro.umontreal.ca> wrote:
>

> AFAIK the SD cards don't support any kind of "tagged command
queuing",
> so after writing the first sector in a sequence,
the card is supposed to
 > be in a state where the write is
completed (even if power goes out at  this
 > particular moment),
so I wonder how they handle this while at the same
 > time being
able to wait for the next write to see if it happens to be
 > to
the next sector.
>

SD cards support a bulk data
transfer or "multiple block write"  operation.  In this
case, it is up to the OS file system driver, device driver and/or SD host 
controller to buffer contiguous writes, and then stream the buffer to  the
SD card with a multiple block write operation. For the most  efficient
writes, you would want your multiple block writes to be  aligned with and
the size of the erase block in the underlying  NAND -- something that the
application committing data would need to be aware of.
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