Re: [iPAQ] File system for a 256MB SD Card

On Thursday 20 February 2003 09:28 am, Jamey Hicks wrote:
> Steven Reddie wrote:
> >I'm not getting any response from the Windows CE community so hoping that
> >someone here may know something about this. An article on slashdot
> > recently mentioned that using FAT file systems with SD cards can lead to
> > sudden death due to the constant writes made to the first bunch of
> > sectors for the allocation table, effectively wearing out only a few
> > critical sectors while leaving the rest of the card ok. Does anyone know
> > if this is a real concern. I can understand why it is, but I don't know
> > if there is some sector translation (vitualisation) going on or something
> > else to make this problem irrelevant. I'm really interested in using it
> > with Windows CE on the iPAQ H5450. It's a Sandisk card if that makes any
> > difference.
>
> I think it really depends on the controller in the Sandisk card, which
> is mapping the SD protocol onto the NAND flash interface. If the
> controller does not do wear leveling, then the cards will not last long.
> Given that most users will be using FAT on the SD, and that the file
> allocation table in the low blocks of the device get updated very often,
> it seems that this is probably not true. If Sandisk is not forthcoming
> with the information, we could devise an experiment to learn whether
> this is true or not -- by reading/writing blocks until the card stops
> working. Case A: read/write random blocks, case B: read/write one
> block, and see how long it takes to fail in each case. Let me know if
> you're interested.
>
> Jamey

FWIW the Sandisk MMC cards do NOT implement wear levelling and Steven's
concerns are very real. I'm also under the impression that Sandisk SD cards
also do not implement wear levelling. Better stick with jffs2 on a Zaurus...

-- 
  Jeff Sutherland, Accelent Systems, Inc.   <http://www.accelent.com>
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