From owner-freebsd-fs@freebsd.org Mon Aug 3 13:50:05 2015 Return-Path: Delivered-To: freebsd-fs@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id D53659B20C1 for ; Mon, 3 Aug 2015 13:50:05 +0000 (UTC) (envelope-from info@pk1048.com) Received: from cpanel61.fastdnsservers.com (server61.fastdnsservers.com [216.51.232.61]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by mx1.freebsd.org (Postfix) with ESMTPS id B5FEE1FCB for ; Mon, 3 Aug 2015 13:50:05 +0000 (UTC) (envelope-from info@pk1048.com) Received: from pool-100-4-179-8.albyny.fios.verizon.net ([100.4.179.8]:49640 helo=[192.168.2.133]) by cpanel61.fastdnsservers.com with esmtpsa (TLSv1:DHE-RSA-AES256-SHA:256) (Exim 4.85) (envelope-from ) id 1ZMEgr-001EqK-Pk; Mon, 03 Aug 2015 07:18:01 -0500 References: <55BC14B7.9010009@sneakertech.com> <9DBE58C6-8C42-498B-AB66-7D9BBDFAA90F@kraus-haus.org> <55BF1270.10003@sneakertech.com> In-Reply-To: <55BF1270.10003@sneakertech.com> Mime-Version: 1.0 (1.0) Content-Type: text/plain; charset=us-ascii Message-Id: <12AA569B-829F-418F-B7B4-897F34B92067@pk1048.com> Content-Transfer-Encoding: quoted-printable X-Mailer: iPad Mail (12H143) From: PK1048 Subject: Re: ZFS: Disabling ARC? Date: Mon, 3 Aug 2015 08:18:00 -0400 To: FreeBSD Filesystems X-AntiAbuse: This header was added to track abuse, please include it with any abuse report X-AntiAbuse: Primary Hostname - cpanel61.fastdnsservers.com X-AntiAbuse: Original Domain - freebsd.org X-AntiAbuse: Originator/Caller UID/GID - [47 12] / [47 12] X-AntiAbuse: Sender Address Domain - pk1048.com X-Get-Message-Sender-Via: cpanel61.fastdnsservers.com: authenticated_id: info@pk1048.com X-Source: X-Source-Args: X-Source-Dir: X-BeenThere: freebsd-fs@freebsd.org X-Mailman-Version: 2.1.20 Precedence: list List-Id: Filesystems List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 03 Aug 2015 13:50:05 -0000 Sent from my portable device On Aug 3, 2015, at 03:04, Quartz wrote: >> If you are really worried about the ARC hogging RAM, then set a cap. >> The kernel tunables here are: >=20 > I'm not worried about it hogging ram per se, but rather I'm a little confu= sed about where and when it helps, where it's useless or detrimental (if eve= r), and consequently I don't really know when I should tune it or what to tu= ne it *to*. > Basically, my question is the subject line of this thread: is there ever a= reason to attempt to disable ARC, and what would that situation probably lo= ok like? I expect that ZFS would be functionally useless (from a performance standpoi= nt) if you completely disabled the ARC, I'm not even sure you can. Take a look at http://www.solarisinternals.com/wiki/index.php/ZFS_Evil_Tunin= g_Guide before doing any ZFS tuning. It was written in the early (Solaris on= ly) days of ZFS, but is still for the most part applicable today. Brendan Gregg has a very good blog entry on the ARC here http://dtrace.org/b= logs/brendan/2012/01/09/activity-of-the-zfs-arc/ I suspect that will answer m= ost of your ARC questions in detail.