From owner-freebsd-questions@FreeBSD.ORG Sat Feb 18 14:29:05 2012 Return-Path: Delivered-To: freebsd-questions@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id E7A5B106566B for ; Sat, 18 Feb 2012 14:29:04 +0000 (UTC) (envelope-from m.seaman@infracaninophile.co.uk) Received: from smtp.infracaninophile.co.uk (smtp6.infracaninophile.co.uk [IPv6:2001:8b0:151:1:3cd3:cd67:fafa:3d78]) by mx1.freebsd.org (Postfix) with ESMTP id 5B2658FC08 for ; Sat, 18 Feb 2012 14:29:04 +0000 (UTC) Received: from seedling.black-earth.co.uk (seedling.black-earth.co.uk [IPv6:2001:8b0:151:1:fa1e:dfff:feda:c0bb]) (authenticated bits=0) by smtp.infracaninophile.co.uk (8.14.5/8.14.5) with ESMTP id q1IESuYZ046841 (version=TLSv1/SSLv3 cipher=DHE-RSA-CAMELLIA256-SHA bits=256 verify=NO) for ; Sat, 18 Feb 2012 14:28:56 GMT (envelope-from m.seaman@infracaninophile.co.uk) X-DKIM: OpenDKIM Filter v2.4.3 smtp.infracaninophile.co.uk q1IESuYZ046841 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=infracaninophile.co.uk; s=201001-infracaninophile; t=1329575336; bh=DdZ7DMaJ8gPdFXUn0s/X4N4z5dnRUwQFa7u7QIO++EY=; h=Message-ID:Date:From:MIME-Version:To:Subject:References: In-Reply-To:Content-Type:Cc; b=n4h8tmPTNT7Jr2iYvWZNGXcm1GT9ImXt+zXp5/qThIQBMdkDHY972TCvU6ClxIJXb EgVU73IaovI3HFgR8TnsrkLbkGTVUEYAKWv21xX/FhbuJAG/srkVH5KydrFoKZ9GUJ vBWSxNM4LbtfwZ9EbJvDqAmHa9t0pfzj9EBU+7zw= Message-ID: <4F3FB5A0.9020806@infracaninophile.co.uk> Date: Sat, 18 Feb 2012 14:28:48 +0000 From: Matthew Seaman User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.6; rv:10.0.2) Gecko/20120216 Thunderbird/10.0.2 MIME-Version: 1.0 To: freebsd-questions@freebsd.org References: <4F3ECF23.5000706@fisglobal.com> <20120217234623.cf7e169c.freebsd@edvax.de> <3D08D03C85ACFBB1ABCDC5DA@mac-pro.magehandbook.com> <20120218112252.772c878b.freebsd@edvax.de> <4F3F80FD.8070201@herveybayaustralia.com.au> <4F3F8A46.1090908@infracaninophile.co.uk> <4F3F8D39.80907@herveybayaustralia.com.au> <4F3FA9FB.7030203@infracaninophile.co.uk> <4F3FAC17.8000300@herveybayaustralia.com.au> In-Reply-To: <4F3FAC17.8000300@herveybayaustralia.com.au> X-Enigmail-Version: 1.3.5 OpenPGP: id=60AE908C Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="------------enigE7D6FF520B8D0D9E72B352D1" X-Virus-Scanned: clamav-milter 0.97.3 at lucid-nonsense.infracaninophile.co.uk X-Virus-Status: Clean X-Spam-Status: No, score=-2.7 required=5.0 tests=ALL_TRUSTED,AWL,BAYES_00, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU autolearn=ham version=3.3.2 X-Spam-Checker-Version: SpamAssassin 3.3.2 (2011-06-06) on lucid-nonsense.infracaninophile.co.uk Subject: Re: /usr/home vs /home X-BeenThere: freebsd-questions@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: User questions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sat, 18 Feb 2012 14:29:05 -0000 This is an OpenPGP/MIME signed message (RFC 2440 and 3156) --------------enigE7D6FF520B8D0D9E72B352D1 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable On 18/02/2012 13:48, Da Rock wrote: > I was thinking along the lines of continuous heavy load of writing (som= e > read) rather large files (5G+ would be average - multiple!) - does that= > warrant caching or is it only lots of smaller files? That and lots of > ~0.5G files (read mostly) is what defines the main load on the system. >=20 > I ask because I'm not 100% sure of what the caching is for. I had > thought it was like the journal log for fast writing to be later writte= n > to the filesystem itself, but now I think I may be wrong in my > judgement. It now sounds like a fast access for usual suspects. >=20 > Now you see how a terabyte and a half disk space can be used in a matte= r > of hours :) Right. That's a lot more file IO than I anticipated in my previous answer. For that amount of usage, 8GB would definitely be required and quite possibly more. Separate devices for ZIL and ARC would be a good idea. (ZIL is effectively the caching for the write path, ARC for the read path. That's a gross over-simplification actually, but good enough.= ) The caching is vital -- it's where all the stuff like checking the parity for a RAIDZn device happens, or the compression/decompression actions. Yes, it works like file system journalling too. Cheers, Matthew --=20 Dr Matthew J Seaman MA, D.Phil. 7 Priory Courtyard Flat 3 PGP: http://www.infracaninophile.co.uk/pgpkey Ramsgate JID: matthew@infracaninophile.co.uk Kent, CT11 9PW --------------enigE7D6FF520B8D0D9E72B352D1 Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG/MacGPG2 v2.0.16 (Darwin) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org/ iEYEARECAAYFAk8/tagACgkQ8Mjk52CukIyzSwCeMrCEsqWRRxcne511oFp6vK8+ WfYAnjz5q74sXTSsaO0qW4PNAn4dPceM =HbCD -----END PGP SIGNATURE----- --------------enigE7D6FF520B8D0D9E72B352D1--