flash device selection

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Bruce Edge Contact options for registered users 's Avatar (by Gravatar) posted on
January 27, 2005, 8:48 pm
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I'm trying to decide on a flash device and filesystem combination for an
embedded device. My concerns are:

- Wear leveling
Does jffs2 wear level across partitions, or just within a partition?
Is the M-Systems hardware leveling controller worth a damn?
Is it preferable to using jffs2?

- log data
How to structure disk layout best to be able to get log data while not
significantly shortening the flash life.

- cost
What's the cheapest device I can get away with.

I need 1-2 GB, almost everything is static, except for log data. I plan
on having a log on/off switch, but I want to be able to log anomalous
events by default.

Thanks, Bruce

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linnix Contact options for registered users 's Avatar (by Gravatar) posted on
January 27, 2005, 10:18 pm
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Re: flash device selection

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an

Wear leveling is usually done in the flash controller, regardless of
the
file system.

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not

If hardware allows it, use a separate (small SLC flash) for log and
everything else read-only (bigger MLC).

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Compact Flash is cheapest.  Less than $200 for 2G.

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plan


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Michael Schnell Contact options for registered users 's Avatar (by Gravatar) posted on
February 4, 2005, 12:11 pm
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Re: flash device selection
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That's a very bad idea. If the file system does not care about wear
leveling and keeps rewriting the same few bytes, the lower level wear
leveling uses up the spare blocks much faster then when using a
flash-aware file system like jff.

-Michael

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