From owner-freebsd-fs@FreeBSD.ORG Fri Oct 11 11:04:11 2013 Return-Path: Delivered-To: freebsd-fs@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [8.8.178.115]) (using TLSv1 with cipher ADH-AES256-SHA (256/256 bits)) (No client certificate requested) by hub.freebsd.org (Postfix) with ESMTP id D18A1F3E for ; Fri, 11 Oct 2013 11:04:11 +0000 (UTC) (envelope-from tevans.uk@googlemail.com) Received: from mail-lb0-x230.google.com (mail-lb0-x230.google.com [IPv6:2a00:1450:4010:c04::230]) (using TLSv1 with cipher ECDHE-RSA-RC4-SHA (128/128 bits)) (No client certificate requested) by mx1.freebsd.org (Postfix) with ESMTPS id 6185B2A7F for ; Fri, 11 Oct 2013 11:04:11 +0000 (UTC) Received: by mail-lb0-f176.google.com with SMTP id y6so3199088lbh.21 for ; Fri, 11 Oct 2013 04:04:09 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=googlemail.com; s=20120113; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type; bh=HEvpc8D1CQ/CRkZ7p9gcCkNfCtDyPVr5979bnwno1SU=; b=t4n2XJuVPMWk5WSOa6hsBzb82MXair7kHn4/WezF73zDNx6fuyHxR0il6VhpHKh3AB cAR11D00meLaIMEuFCkfdK3qKew6+TsdmJ48iBZs463E+3sPHvozPn02Vir6qtC5JumO GKDvP6FNOCW3xYLNiBBLN06v11Ej7R+EvKXmHhvbFK/qC6w11roncUAyLalXfraauyiU 30eNafz8m4/gx3PxQuCTQMIUisEqXniSHH0f05qeqYBPYUaKsddnYPrsyrsB/oaRLURs 7btHsu7fH6sIpIObiuQq8XGf3PdOLacA3U3U9eCt8u+OyrgZ5uC/ydBDr2pHUpu+Rnmw zGQw== MIME-Version: 1.0 X-Received: by 10.152.171.72 with SMTP id as8mr1231557lac.33.1381489449417; Fri, 11 Oct 2013 04:04:09 -0700 (PDT) Received: by 10.112.170.70 with HTTP; Fri, 11 Oct 2013 04:04:09 -0700 (PDT) In-Reply-To: <20131010170724.GA19751@potato.growveg.org> References: <20131010170724.GA19751@potato.growveg.org> Date: Fri, 11 Oct 2013 12:04:09 +0100 Message-ID: Subject: Re: RAM and zfs and multiple disks From: Tom Evans To: john@potato.growveg.org Content-Type: text/plain; charset=UTF-8 Cc: FreeBSD FS X-BeenThere: freebsd-fs@freebsd.org X-Mailman-Version: 2.1.14 Precedence: list List-Id: Filesystems List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 11 Oct 2013 11:04:11 -0000 On Thu, Oct 10, 2013 at 6:07 PM, John wrote: > Hello list, > > I'd like to have zfs on my freebsd desktop. However, > this motherboard can take 8GB RAM, max. > > I'd like to get 2 x4Tb drives. Realistically, do I > need another motherboard? The primary reason to have ZFS > is to guard against bitrot. > My home ZFS file server is a Core2 Duo with 8GB of RAM and has 12 x 1.5TB arranged in 2 x 6 disk raidz, and before the second set of disks were added it ran with only 2 GB just fine. The only ZFS setting I "had" to tweak was to limit ARC to 4 GB, in order to have plenty of free RAM: vfs.zfs.arc_max="4294967296" I say "had to", because I didn't really, I just prefer not having the ARC taking all free RAM and releasing as necessary. Depending upon your usage, you may find that the ARC is not terribly useful anyway, eg in my case there is 4 GB of ARC covering 14336 GB of data, and since my data is mainly archived binary data, I'm unlikely to re-use the same data twice in one day. Where the ARC really comes in handy for me is prefetch, loading large files into the ARC as I start reading them. Prefetching is disabled if you have less than 4 GB of RAM. Cheers Tom