From owner-freebsd-fs@freebsd.org Tue Aug 4 07:28:56 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 370129B3AF7 for ; Tue, 4 Aug 2015 07:28:56 +0000 (UTC) (envelope-from alexander@leidinger.net) Received: from mail.ebusiness-leidinger.de (mail.ebusiness-leidinger.de [217.11.53.44]) (using TLSv1.2 with cipher DHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by mx1.freebsd.org (Postfix) with ESMTPS id DB243130D for ; Tue, 4 Aug 2015 07:28:55 +0000 (UTC) (envelope-from alexander@leidinger.net) Received: from outgoing.leidinger.net (p57BB94CE.dip0.t-ipconnect.de [87.187.148.206]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by mail.ebusiness-leidinger.de (Postfix) with ESMTPSA id 2508483E402; Tue, 4 Aug 2015 09:28:21 +0200 (CEST) Received: from webmail.leidinger.net (webmail.Leidinger.net [IPv6:fd73:10c7:2053:1::3:102]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by outgoing.leidinger.net (Postfix) with ESMTPS id 12BE110AF; Tue, 4 Aug 2015 09:28:18 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=leidinger.net; s=outgoing-alex; t=1438673298; bh=FANboUP9iEkytN6JfWJ9cSAhkJbFJ0/lwLOJ7qWL+Rw=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=1JOYAYCVNk9y0gij4AMuX6GDAQEcPUZV9fGJ7X2L6tUn82t/ivAJxmVlShK68jqL9 YQ+YpO6PYlb/pMWytEtZrSjpyYVw+9zia3Ku526gEewXM3HsQwmdMdyUAiAJDRyiU+ 078TFlEUQCF+sofun6RcTkgEIwGiK4+eg0t4hca8ju06SpunSrDRriGNZ4QKtFpcW+ K6urzTcI5j7CX4GqdXZMeJHzlEodEporUxSpbMdMN5eA0GmQnOfxGHtBb/OyK9HLv6 rXv2AQOepgLOMcQA+ElVXHoYWYrx442T9v6/C8tt/AYQFz7TRsYxzeHtmZkoEshb+g vKlQQp1LyOSJA== Received: (from www@localhost) by webmail.leidinger.net (8.14.9/8.14.4/Submit) id t747SHS9055842; Tue, 4 Aug 2015 09:28:17 +0200 (CEST) (envelope-from Alexander@leidinger.net) X-Authentication-Warning: webmail.leidinger.net: www set sender to Alexander@leidinger.net using -f Received: from 217.197.101.97 ([217.197.101.97]) by webmail.leidinger.net (Horde Framework) with HTTP; Tue, 04 Aug 2015 09:28:17 +0200 Date: Tue, 04 Aug 2015 09:28:17 +0200 Message-ID: <20150804092817.Horde.aha5Ph2llansySR3xJXVMN2@webmail.leidinger.net> From: Alexander Leidinger To: Matt Churchyard Cc: Quartz , FreeBSD FS Subject: Re: ZFS: Disabling ARC? References: <55BC14B7.9010009@sneakertech.com> <20150801133635.00002ecc@Leidinger.net> <45e74b89dd754991a366a46aa5101822@SERVER.ad.usd-group.com> In-Reply-To: <45e74b89dd754991a366a46aa5101822@SERVER.ad.usd-group.com> User-Agent: Horde Application Framework 5 Content-Type: text/plain; charset=utf-8; format=flowed; DelSp=Yes MIME-Version: 1.0 Content-Disposition: inline X-EBL-MailScanner-Information: Please contact the ISP for more information X-EBL-MailScanner-ID: 2508483E402.AFFBD X-EBL-MailScanner: Found to be clean X-EBL-MailScanner-SpamCheck: not spam, spamhaus-ZEN, SpamAssassin (not cached, score=-0.1, required 6, autolearn=disabled, DKIM_SIGNED 0.10, DKIM_VALID -0.10, DKIM_VALID_AU -0.10) X-EBL-MailScanner-From: alexander@leidinger.net X-EBL-MailScanner-Watermark: 1439278101.55458@adi5cCj9+tZ6rdPkUh3VEg X-EBL-Spam-Status: No 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: Tue, 04 Aug 2015 07:28:56 -0000 Quoting Matt Churchyard (from Mon, 3 Aug 2015 15:00:07 +0000): > I don't know if it's changed, but even changing ARC to metadata only > used to cause massive performance issues when reading large files in > small chunks. Reading a 128k ZFS record in 4k chunks would cause ZFS > to read the same 128k record from disk 32 times. > There's a forum thread about it here - > https://forums.freebsd.org/threads/zfs-primarycache-all-versus-metadata.45555/ When using "metadata" as the setting, you tell that you are OK to trade in some (data access, not metadata-access) performance for memory. Determining if the resulting performance is acceptable is up to you. If you blindly set the value without validating that it is OK for you, you shall not complain (= "measure, change, measure" and not "measure, change, hope"). I agree that not for all changes the resulting effects are 100% obvious and explicitely stating the edge-cases is appreciated. Feel free to add some words about it to https://wiki.freebsd.org/ZFSTuningGuide Bye, Alexander. -- http://www.Leidinger.net Alexander@Leidinger.net: PGP 0xC773696B3BAC17DC http://www.FreeBSD.org netchild@FreeBSD.org : PGP 0xC773696B3BAC17DC