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Subject: Re: What append when arc full
To: Albert Shih <Albert.Shih@obspm.fr>, freebsd-fs@freebsd.org
References: <20180613200700.GA3156@io.chezmoi.fr>
From: Shane Ambler <FreeBSD@ShaneWare.Biz>
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Date: Thu, 14 Jun 2018 13:06:07 +0930
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On 14/06/2018 05:37, Albert Shih wrote:
> Hi everyone
> 
> 
> On one of my server I need to reserve some ram to the application.
> 
> So I would like to know what's happend when the ARC are full.

ARC is a cache and it will use any unused ram that it can. When a
process makes a memory request some of the ARC can be released to
satisfy the request. This can add a delay to a process starting, which
is not always desirable.

If you want to keep some ram free for your processes, then you can set
vfs.zfs.arc_max to limit the ram used by ARC. On recent system versions
you can change it dynamically using sysctl or you can set it in
/boot/loader.conf to set it at startup, it accepts human units so you
can use vfs.zfs.arc_max=25G


-- 
FreeBSD - the place to B...Storing Data

Shane Ambler