Follow-up to wearing / caching question

Martin Egholm Nielsen martin at
Mon Feb 7 16:36:45 EST 2005

Hi there,

>> I've been tasked with approximating the lifespan of the flash
>> (JFFS2) filesystem embedded in our products. Is there a best method
>> for calculating the space required for a fixed-size file over a
>> given lifespan? If we want our flash filesystem to be available for
>> an approximate lifespan of 20 years, given the wear-leveling
>> duty-cycle of JFFS2, and an average block endurance of 100k 
>> write/erase cycles, would I need 150% of the file's size? 200%?
>> 1000%?
=== 8< 8< 8< ===
> Another way to look at it is an imaginary 1MiB flash.  You can write
> it 100k times, for a total of 100GiB written to it.  With 600M seconds
> in your expected 20 years, that gives you ~160 Bytes/s average write
> speed.  Not very much.
Then what about the pagesize and corresponding writebuffer - this may 
have an effect, as well, when talking that slow write rates, right?!

> Is that the calculation you were looking for?
I liked it alot - thanks! ;-)

// Martin

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