From mboxrd@z Thu Jan  1 00:00:00 1970
Message-ID: <7738cc425fad5f8b56882b45df4fdf6d@swtch.com>
To: 9fans@cse.psu.edu
Subject: Re: [9fans] Clearing venti arena during install
From: "Russ Cox" <rsc@swtch.com>
Date: Sun, 26 Mar 2006 19:33:18 -0500
In-Reply-To: <20060327002355.F4015294E8@mail.bitblocks.com>
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> Creating a hole is as easy as seeking beyond the end of a
> file and scribbling something but maintaining its holeyness
> by checking every write for a block of zeroes is quite
> expensive.

It only needs to be done when writing to a hole,
and for the small cost of a scan over the block,
you get to avoid a few disk writes (more expensive).
It's worth doing.

Aux/disksim does this, specifically so that I can run
tests on enormous files without needing the backing
store.  For example, that's how I checked tar's
recently-added support for files > 4GB.

Russ