From owner-freebsd-hackers@FreeBSD.ORG Mon May 4 20:05:18 2009 Return-Path: Delivered-To: freebsd-hackers@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 7E5C4106564A for ; Mon, 4 May 2009 20:05:18 +0000 (UTC) (envelope-from mat.macy@gmail.com) Received: from yw-out-2324.google.com (yw-out-2324.google.com [74.125.46.31]) by mx1.freebsd.org (Postfix) with ESMTP id 366F68FC08 for ; Mon, 4 May 2009 20:05:18 +0000 (UTC) (envelope-from mat.macy@gmail.com) Received: by yw-out-2324.google.com with SMTP id 9so2501807ywe.13 for ; Mon, 04 May 2009 13:05:17 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:mime-version:sender:received:in-reply-to :references:date:x-google-sender-auth:message-id:subject:from:to:cc :content-type:content-transfer-encoding; bh=s5DIfk/aqmuAgypheE4H5A03F45i35LvIrjqAkBSiD4=; b=H14fbPo1AzD6SEr9O+m7LgycgOuC6Rz7OV9bbgyML3BaPT7zOj+rRua/pd9ekwI4xj UcU8m0lvzNiLTaygbaebp0tL+AU6SQLmOSfG8tnub6tWw7SxegMzFa2OlXVyTFiecbw/ notpO44tXGP9wCgr0L3aaQ2yS3CA6QLxdftE0= DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:sender:in-reply-to:references:date :x-google-sender-auth:message-id:subject:from:to:cc:content-type :content-transfer-encoding; b=p6bU43SctRR/4pFpjohP6SMUwPS6Vj4QuBiDpM7fjbSdacCv5l00JRX4amNPdnAP7l AlchzguhulZsq/khQlgQnrPrB+VcKb7hPczvaSPKebkm/+Ev+wVhY16nBPEImylGQCwC xpwEWCx2OztpmpzayuB5x8mtbdwcVhzAu3LoI= MIME-Version: 1.0 Sender: mat.macy@gmail.com Received: by 10.100.229.12 with SMTP id b12mr13912174anh.26.1241467517598; Mon, 04 May 2009 13:05:17 -0700 (PDT) In-Reply-To: <49FF21E7.4060201@datapipe.com> References: <49FF21E7.4060201@datapipe.com> Date: Mon, 4 May 2009 13:05:17 -0700 X-Google-Sender-Auth: d4fda1022e6fb917 Message-ID: <3c1674c90905041305g285b4609icd7435d436d3bbe0@mail.gmail.com> From: Kip Macy To: msaad@datapipe.com Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Cc: "freebsd-hackers@freebsd.org" Subject: Re: ZFS ARC Cache: What is the lowest tested size X-BeenThere: freebsd-hackers@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Technical Discussions relating to FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 04 May 2009 20:05:18 -0000 On Mon, May 4, 2009 at 10:12 AM, Mark Saad wrote: > > Hello List > =A0 Worked on breaking ZFS we came across a interesting question; > What is the lowest tested ZFS ARC Cache size ? I haven't tested it with just over 64MB, but the code indicates that that is the lowest you should try. http://src.opensolaris.org/source/xref/onnv/onnv-gate/usr/src/uts/common/fs= /zfs/arc.c 3500 /* 3501 * Allow the tunables to override our calculations if they are 3502 * reasonable (ie. over 64MB) 3503 */ 3504 if (zfs_arc_max > 64<<20 && zfs_arc_max < physmem * PAGESIZE) 3505 arc_c_max =3D zfs_arc_max; 3506 if (zfs_arc_min > 64<<20 && zfs_arc_min <=3D arc_c_max) 3507 arc_c_min =3D zfs_arc_min; >Also could you reliably > run with it set to 0 ? For better and worse, ZFS isn't primarily a file system. It is a transactional object store that has a file system as one type of object. The ARC is not a file system buffer cache, it caches virtual device blocks. You might think of it as being more like a very large write-back drive cache. It might work with less than 64MB, but the ARC buffers are what ZIO sends down to disk so it certainly would not work with zero. Cheers, Kip