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Date:      Thu, 14 Jun 2018 17:01:29 +1000
From:      Peter Jeremy <peter@rulingia.com>
To:        Albert Shih <Albert.Shih@obspm.fr>
Cc:        freebsd-fs@freebsd.org
Subject:   Re: What append when arc full
Message-ID:  <20180614070129.GE88895@server.rulingia.com>
In-Reply-To: <20180614054333.GA7053@io.chezmoi.fr>
References:  <20180613200700.GA3156@io.chezmoi.fr> <248ad0be-2002-89b5-0c1a-3ac73d493149@ShaneWare.Biz> <20180614054333.GA7053@io.chezmoi.fr>

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On 2018-Jun-14 07:43:33 +0200, Albert Shih <Albert.Shih@obspm.fr> wrote:
>But my concern are what append if I shrink a little more the arc_max, let's
>say 64G knowing I got < 30To of data. Does I'm going to loose lot of
>performance ?

This really depends on your workload and the disk access pattern.  I
suggest you install sysutils/zfs-stats and look at the various ARC
hit/miss rates once your system has stabilised.  You might find that
tuning vfs.zfs.arc_meta_limit can also help - by default, it's 1/4
of ARC but in my experience, metadata misses are more expensive so
increasing that can help.

--=20
Peter Jeremy

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