Lifetime of flash memory

[John Richard Moser <nigelenki@comcast.net>]

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I have a kind of dumb question.  I keep hearing that "USB Flash Memory"
or "Compact Flash Cards" and family have "a limited number of writes"
and will eventually wear out.  Recommendations like "DO NOT PUT A SWAP
FILE ON USB MEMORY" have come out of this.  In fact, quoting
Documentation/laptop-mode.txt:

  * If you're worried about your data, you might want to consider using
    a USB memory stick or something like that as a "working area". (Be
    aware though that flash memory can only handle a limited number of
    writes, and overuse may wear out your memory stick pretty quickly.
    Do _not_ use journalling filesystems on flash memory sticks.)

The question I have is, is this really significant?  I have heard quoted
that flash memory typically handles something like 3x10^18 writes; and
that compact flash cards, USB drives, SD cards, and family typically
have integrated control chipsets that include wear-leveling algorithms
(built-in flash like in an iPaq does not; hence jffs2).  Should we
really care that in about 95 billion years the thing will wear out
(assuming we write its entire capacity once a second)?

I call FUD.

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