linux-kernel - Re: Zero-clearing all zero-clearable bytes.

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Message-ID: <4928DBAF.4030209@lougher.demon.co.uk>
Date:	Sun, 23 Nov 2008 04:27:27 +0000
From:	Phillip Lougher <phillip@...gher.demon.co.uk>
To:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
CC:	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: Zero-clearing all zero-clearable bytes.

Tetsuo Handa wrote:
> Hello.
> 
> I often create a Live CD.
> When creating a Live CD, loopback mounted ext3 image files are used.
> These image files are then compressed so that the ISO image will fit within
> a CD-R's capacity (i.e. 700MB).
> 

You don't mention what you're using to compress the ext3 image file.  If 
you're using Squashfs then it's much better to zero-fill the blocks 
rather than use 255, because Squashfs detects zero-filled blocks and 
stores them sparsely.  This not only gets slightly better compression 
(than a compressed zero-filled block), but reading is also slightly faster.

Phillip

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