From owner-freebsd-fs@freebsd.org Mon Aug 3 07:04:24 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 7B0599B20BA for ; Mon, 3 Aug 2015 07:04:24 +0000 (UTC) (envelope-from quartz@sneakertech.com) Received: from douhisi.pair.com (douhisi.pair.com [209.68.5.179]) (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 59B4F160C for ; Mon, 3 Aug 2015 07:04:24 +0000 (UTC) (envelope-from quartz@sneakertech.com) Received: from [10.2.2.1] (pool-173-48-121-235.bstnma.fios.verizon.net [173.48.121.235]) by douhisi.pair.com (Postfix) with ESMTPSA id 35B383F7C4 for ; Mon, 3 Aug 2015 03:04:17 -0400 (EDT) Message-ID: <55BF1270.10003@sneakertech.com> Date: Mon, 03 Aug 2015 03:04:16 -0400 From: Quartz MIME-Version: 1.0 To: freebsd-fs@freebsd.org Subject: Re: ZFS: Disabling ARC? References: <55BC14B7.9010009@sneakertech.com> <9DBE58C6-8C42-498B-AB66-7D9BBDFAA90F@kraus-haus.org> In-Reply-To: <9DBE58C6-8C42-498B-AB66-7D9BBDFAA90F@kraus-haus.org> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit 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 07:04:24 -0000 > If you are really worried about the ARC hogging RAM, then set a cap. > The kernel tunables here are: I'm not worried about it hogging ram per se, but rather I'm a little confused about where and when it helps, where it's useless or detrimental (if ever), and consequently I don't really know when I should tune it or what to tune 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 look like? > Please note that I have never seen a _panic_ due to ARC RAM issues, I > have had systems starved for RAM for periods and processes (VMs) get > very angry, but the system as a whole usually recovers. I then > restart the processes that got angry. I didn't mean panics specifically due to ARC, but that in the process of reading various threads about memory related panics and ARC memory issues (separately) I realized that I wasn't really clear about memory management on FreeBSD and how ARC interacted there.