linux-kernel - Re: [RFC/PATCH 0/1] ubi: Add ubiblock driver

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Message-ID: <20121121110022.35db364f@skate>
Date:	Wed, 21 Nov 2012 11:00:22 +0100
From:	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>
To:	Ezequiel Garcia <elezegarcia@...il.com>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-mtd@...ts.infradead.org,
	Artem Bityutskiy <dedekind1@...il.com>,
	David Woodhouse <dwmw2@...radead.org>,
	Tim Bird <tim.bird@...sony.com>,
	Michael Opdenacker <michael.opdenacker@...e-electrons.com>
Subject: Re: [RFC/PATCH 0/1] ubi: Add ubiblock driver

Dear Ezequiel Garcia,

On Tue, 20 Nov 2012 19:39:38 -0300, Ezequiel Garcia wrote:

> * Read/write support
> 
> Yes, this implementation supports read/write access.

While I think the original ubiblk that was read-only made sense to
allow the usage of read-only filesystems like squashfs, I am not sure a
read/write ubiblock is useful.

Using a standard block read/write filesystem on top of ubiblock is going
to cause damage to your flash. Even though UBI does wear-leveling, your
standard block read/write filesystem will think it has 512 bytes block
below him, and will do a crazy number of writes to small blocks. Even
though you have a one LEB cache, it is going to be defeated quite
strongly by the small random I/O of the read/write filesystem.

I am not sure letting people use read/write block filesystems on top of
flashes, even through UBI, is a good idea.

Thomas
-- 
Thomas Petazzoni, Free Electrons
Kernel, drivers, real-time and embedded Linux
development, consulting, training and support.
http://free-electrons.com
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