From mboxrd@z Thu Jan  1 00:00:00 1970
From: Mike Snitzer <snitzer@redhat.com>
Subject: Re: Does dm-thin support GC (garbage collection) ?
Date: Wed, 9 May 2012 09:47:11 -0400
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On Wed, May 09 2012 at  2:03am -0400,
Busby <chaimvy@gmail.com> wrote:

> I created pool without ignore_discard feature, is this the way to
> enable discard? I mounted the ext4 with '--discard' args, I will trace
> whether the ext4 really issue discard later.

thin-pool's discard support (and discard passdown) are enabled by
default.  But again, if the underlying storage doesn't support discards
you'll get this warning when you load the thin-pool's table:

device-mapper: thin: Discard unsupported by data device: Disabling discard passdown.