Re: Flash device types

Mark Rustad
2005-05-13T18:56:29Z

On May 13, 2005, at 1:26 PM, Lennart Sorensen wrote:

> Not really. I believe sandisk has wear leveling on the 201 series CF
> cards and on their new generation CF/SD for sure they have it (and
> unfortunately for us they discontinued industrial temperature in the
> new
> line so we have had to look elsewhere for CF cards).
>
> Unfortunately a lot of what is sold to consumers at retail is cheap
> crap. :)

It does seem to be a problem finding out how things really work in
these devices. There seem to be the following types (from worst to
best):

1. No wear leveling. Bad blocks are mapped out at manuf. time and that
is it.
2. Bad blocks are detected and remapped dynamically. This is sometimes
called wear-leveling, but the device life is a function of how many
spares there originally were.
3. "Real" wear leveling. This can move data to fully use the life of
all sectors.
4. "Real" wear leveling with lots of optimization and write cache -
these are large devices usually with the ability to have battery power
to ensure write cache can be flushed out.

#4 is easy to determine because of the size and complexity of the
things. The others are much harder to distinguish and it really is
important to know what you are dealing with. If you can't find out how
it works, I would assume #1 or #2 which are both pretty poor.

It really would be nice to easily find out what category of device
these things really are.

--
Mark Rustad, MRustad@mac.com