Date: Thu, 14 Jun 2018 08:28:18 +0200 From: Ben RUBSON <ben.rubson@gmail.com> To: Tom Evans via freebsd-fs <freebsd-fs@freebsd.org> Subject: Re: What append when arc full Message-ID: <842D180A-4725-418D-8EF8-639B50C8B72D@gmail.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 14 Jun 2018 07:43, Albert Shih wrote: > I try last night, if I put > > vfs.zfs.arc_max=96G > > everything work fine (the sending). So I think that's the point. > > 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 ? The least recently used buffers of (meta)data (the colder ones) will be evicted to make room for the new needed (meta)data buffers. ZFS has a "constantly" background job running to keep ARC size under the limit. Performance will of course depend on the amount of hot (meta)data you play with. Perhaps you could benefit from setting a L2ARC with your 2 SSDs. Evicted buffers would then be stored there for faster access when needed. >> 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 > > "dynamically" .... I though it's only can set at boot time I also have it in /etc/sysctl.conf on 11.0 systems, I think it was also the case with 10.3. Ben
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