From owner-freebsd-geom@FreeBSD.ORG  Tue Jan  7 12:10:11 2014
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Date: Tue, 07 Jan 2014 13:10:06 +0100
From: Miroslav Lachman <000.fbsd@quip.cz>
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To: Steven Hartland <killing@multiplay.co.uk>
Subject: Re: Is TRIM working with gmirror?
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Cc: Karl Pielorz <kpielorz_lst@tdx.co.uk>, freebsd-geom@FreeBSD.org
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Steven Hartland wrote:
[...]
> Unless you have a specific reason for using gmirror I would strongly
> advise trying ZFS instead, it will definitely support TRIM in that
> config and comes with a host of other benefits too :)

The specific reason is performance and memory consumption. We need every 
piece of performance and all memory to MySQL daemon, so this is why 
gmirror was choosen.
We have ZFS on other purposes machines for years (from 7.x days), so I 
can say "I have a lot of experiences" (good and bad too).
In some tests, ZFS is about 50% slower than UFS.

What about graid(8) mirror instead of gmirror(8)? Is there better 
support for TRIM on UFS?

Miroslav Lachman