Re: Lifetime of flash memory

[Joshua Kugler <joshua.kugler@uaf.edu>]

On Tuesday 21 March 2006 08:01, John Richard Moser wrote:
> 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.

Search for a thread on LKML having to do with enabling "sync" on removable 
media, especially VFAT media.  If you are copying a large file, and the FAT 
on the device is being updated with every block, you can literally fry your 
device in a matter of minutes, because the FAT is always in the same spot, 
thus it is always overwriting the same spot.

j----- k-----

-- 
Joshua Kugler                 PGP Key: http://pgp.mit.edu/
CDE System Administrator             ID 0xDB26D7CE
http://distance.uaf.edu/
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