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On Tue, Aug 31, 2010 at 5:47 AM, Stefan Monnier wrote:
> Could be. That depends on the particular card you use, tho,since the
> algorithm used by the translation layer varies.
The only relevant thing that varies from SD card to SD card is
the size of the erase block. Any re-mapping SDs (and
most SSDs) do are at the erase block level.
Wear
leveling algorithms vary -- but as far as I know, the majority are
still based around the erase block. (e.g.: When a group of sectors
written are smaller than the size of an erase block, the remaining
sectors are read from the erase block, combined with the new data, and
then written to a free block with the lowest amount of writes.)I'm interested in seeing an SD card that remaps at a finer grain than
its erase block.
> Wear leveling algorithms vary -- but as far as I know, the majority
> are still based around the erase block. (e.g.: When a group of
> sectors written are smaller than the size of an erase block, the
> remaining sectors are read from the erase block, combined with the
> new data, and then written to a free block with the lowest amount
> of writes.)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.
Stefan