Message-ID: <4287E807.6070502@rtr.ca>
Date: Sun, 15 May 2005 20:23:35 -0400
From: Mark Lord <lkml@rtr.ca>
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To: Denis Vlasenko <vda@ilport.com.ua>
Cc: mhw@wittsend.com, linux-kernel@vger.kernel.org
Subject: Re: Sync option destroys flash!
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All flashcards (other than dumb "smart media" cards) have integrated
NAND controllers which perform automatic page/block remapping and
which implement various wear-leveling algorithms.  Rewriting "Sector 0"
10000 times probably only writes once to the first sector of a 1GB card.
The other writes are spread around the rest of the card, and remapped
logically by the integrated controller.

Linux could be more clever about it all, though.  Wear-leveling can only
be done efficiently on "unused" or "rewritten" blocks/pages on the cards,
and not so well with areas that hold large static data files (from the point
of view of the flash controller, not the O/S).

If we were really clever about it, then when Linux deletes a file from a
flashcard device, it would also issue CFA ERASE commands for the newly
freed sectors.  This would let the card's controller know that it can
remap/reuse that area of the card as it sees fit.

But it's dubious that a *short term* use (minutes/hours) of O_SYNC
would have killed a new 1GB card.

Cheers
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