From mboxrd@z Thu Jan  1 00:00:00 1970
Date: Tue, 20 Oct 2020 18:02:52 +0100
From: Alasdair G Kergon <agk@redhat.com>
Message-ID: <20201020170252.GA5698@agk-dp.fab.redhat.com>
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Subject: Re: [linux-lvm] Why does thinpool take 2*poolmetadatasize space?
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To: Scott Moser <smoser@brickies.net>
Cc: linux-lvm@redhat.com

On Tue, Oct 20, 2020 at 12:33:41PM -0400, Scott Moser wrote:
> When I create an lvmthinpool with size S and poolmetadatasize P,
> it reduces the available freespace by S+2P. I expected that to
> be S+P. Where did the extra poolmetadatasize get used?

So that you have sufficient disk space to store a second copy of it
if you need to perform any work on the metadata in future.

Recovery operations, for example, create a recovered copy in that
'spare' space then swap to use it leaving the space used by the
original metadata as the new 'spare'.

Alasdair