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Date: Fri, 04 Feb 2011 14:12:03 +0000
From: "Bryn M. Reeves" <bmr@redhat.com>
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Subject: [linux-lvm] lvm2: zeroing free space
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To: LVM general discussion and development <linux-lvm@redhat.com>

Hi Folks,

Recently had a query from someone using an array supporting thin provisioning
with zero page reclaim[1].

They wanted a method to write zeros to all the unallocated space in a VG to
trigger a reclaim of unused regions in the VG's PVs.

My suggestion was to lvcreate a -l100%FREE LV named "filler" and overwrite it
from /dev/zero.

It seems like this might something a lot of users want as this functionality
gets to be more common.

I wondered if it could be worth adding a script to automate this or even an
option to vgchange (e.g. --zero-free-space)?

Didn't have time to try putting anything together yet but it seems such a
feature could be useful.

Regards,
Bryn.

[1] http://blogs.hds.com/hu/2009/03/zero-page-reclaim.html