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To: Bryan Andersen <bryan@bogonomicon.net>
Cc: Pavel Machek <pavel@ucw.cz>, kernel list <linux-kernel@vger.kernel.org>
Subject: Re: Compactflash cards dying?
From: "Martin K. Petersen" <mkp@mkp.net>
Organization: mkp.net
References: <20030202223009.GA344@elf.ucw.cz>
	<3E3E1643.2080807@bogonomicon.net>
Date: 03 Feb 2003 09:08:49 -0500
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>>>>> "Bryan" == Bryan Andersen <bryan@bogonomicon.net> writes:

Bryan> Use a file system that is designed for use on FLASH devices.
Bryan> In general FLASH devices are not very useable for systems that
Bryan> need to modify data on the disk often.

Just a heads up that flash (as in MTD) != Compact Flash.

For all practical purposes a Compact Flash is an IDE disk (Or a an IDE
controller with a disk behind it.  Depends how you wire it).

Internally, the Compact Flash does all the wear averaging that a flash
filesystem like jffs2 provides.  Transparently to the application.

All Linux sees is a linear stream of bytes.  Just like a disk.  And it
should be treated as such.


Bryan> You may wish to look at the virtual memory file system
Bryan> available in the kernel if you have enough RAM.  You would
Bryan> mount your CompactFlash device read only and have all updates
Bryan> go to the virtual memory filesystem. When you want to commit
Bryan> the changes, remount the CompactFlash read/write and save the
Bryan> changes then remount it read only.

tmpfs to the rescue!


Bryan> You would be surprised how fast a million writes can happen on
Bryan> a disk.

Yup.

You would also be surprised how long it takes to actually *perform* a
million writes on a slow piece of media like Compact Flash ;)

-- 
Martin K. Petersen	Wild Open Source, Inc.
mkp@wildopensource.com	http://www.wildopensource.com/
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