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> I'm considering to use JFFS for our openhardware board
> (http://www.openhardware.net/Dragonix) . I want to append 10 bytes
> to a log every 6 seconds. I would like to use any kind of flash with
> NOR or NAND technology. Let's assume that the chips have 1 million
> Program / Erase Cycles and a 2megabyte chip. How log will it take
> until the chips is blown? When writing the same location it will take
> about 70 days, which is pretty short. We need at least 5 years.
If you have a 2 MiB chip and you append 10 bytes of data each 6 seconds,
then even assuming no metadata overhead you'll fill the chip in just over a
fortnight. Presumably you'll be periodically reading these logs and erasing
them from the flash?
An estimated chip lifetime of 1 million erase cycles then means it should
last 1 million * 14.5 days, or about 38 thousand years.
With ten-byte writes, you'll find that there's actually quite a lot of
metadata overhead though - for this purpose you might do better to log
directly to the raw flash device.
> How does a chip die? Does JFFS handle defect sectors?
JFFS doesn't handle bad sectors, and will have a tough time working round
them due to the sequential nature of the log. The folks at Lynuxworks have
worked around this by adding a kind of translation layer underneath JFFS,
to map out the bad sectors.
JFFS2 can deal with bad sectors to a certain extent - but this code hasn't
been tested hard because of the infrequency of such events.
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- From: Daniel Haensse <email@example.com>