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Date: Thu, 24 Jan 2013 23:42:35 +0000
From: Alasdair G Kergon <agk@redhat.com>
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Subject: Re: [linux-lvm] Sparse LVs, --virtualsize equal to --size
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To: LVM general discussion and development <linux-lvm@redhat.com>

So look at thin provisioning with its zeroing option.
External origin.  (support currently being added to lvm)

Or this not-yet-upstream target:
http://people.redhat.com/agk/patches/linux/editing/dm-add-zeroed-target.patch

Alasdair