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

I was wondering if the software on the iPAQ did the wear-leveling but I
guess it's not possible for it to do it in some way that wouldn't make the
card unreadable on some other device. Sounds like installing something like
YAFFS is the only way to go, or treat it as almost write-once storage.

Steven

-----Original Message-----
From: ipaq-bounces@handhelds.org [mailto:ipaq-bounces@handhelds.org]On
Behalf Of Jamey Hicks
Sent: Friday, 21 February 2003 1:28 AM
To: Steven Reddie
Cc: ipaq@handhelds.org
Subject: Re: [iPAQ] File system for a 256MB SD Card

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

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Received on Thu Feb 20 23:24:32 2003