From owner-freebsd-fs@FreeBSD.ORG Wed Aug 14 15:29:17 2013 Return-Path: Delivered-To: fs@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) (using TLSv1 with cipher ADH-AES256-SHA (256/256 bits)) (No client certificate requested) by hub.freebsd.org (Postfix) with ESMTP id 27F80BD3 for ; Wed, 14 Aug 2013 15:29:17 +0000 (UTC) (envelope-from wjw@digiware.nl) Received: from smtp.digiware.nl (unknown [IPv6:2001:4cb8:90:ffff::3]) (using TLSv1 with cipher ADH-CAMELLIA256-SHA (256/256 bits)) (No client certificate requested) by mx1.freebsd.org (Postfix) with ESMTPS id DB8492227 for ; Wed, 14 Aug 2013 15:29:16 +0000 (UTC) Received: from rack1.digiware.nl (unknown [127.0.0.1]) by smtp.digiware.nl (Postfix) with ESMTP id 2049E153435; Wed, 14 Aug 2013 17:29:15 +0200 (CEST) X-Virus-Scanned: amavisd-new at digiware.nl Received: from smtp.digiware.nl ([127.0.0.1]) by rack1.digiware.nl (rack1.digiware.nl [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id HWy7bahRmprP; Wed, 14 Aug 2013 17:29:14 +0200 (CEST) Received: from [IPv6:2001:4cb8:3:1:1db2:7fa3:18b1:b05b] (unknown [IPv6:2001:4cb8:3:1:1db2:7fa3:18b1:b05b]) by smtp.digiware.nl (Postfix) with ESMTP id F39CF15343A; Wed, 14 Aug 2013 17:29:13 +0200 (CEST) Message-ID: <520BA249.8030603@digiware.nl> Date: Wed, 14 Aug 2013 17:29:13 +0200 From: Willem Jan Withagen Organization: Digiware Management b.v. User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:17.0) Gecko/20130801 Thunderbird/17.0.8 MIME-Version: 1.0 To: Bob Friesenhahn Subject: Re: Fwd: Disk scheduling activity... References: <520B8B1E.7060002@digiware.nl> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: fs@freebsd.org X-BeenThere: freebsd-fs@freebsd.org X-Mailman-Version: 2.1.14 Precedence: list List-Id: Filesystems List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 14 Aug 2013 15:29:17 -0000 On 2013-08-14 16:03, Bob Friesenhahn wrote: > On Wed, 14 Aug 2013, Willem Jan Withagen wrote: >> >> Just a point of information or curiosity, and I don't think/know if it >> is any problem... >> >> I have the raidz array with 8 disks, which I'm using to backup to. >> It is configured >> 4 disks on a mvs controller >> 4 disks on an Areca controller (JBODs with battery) >> Both controllers are on a PCI-E slot >> >> Most of the time the source just fully loads the pipe and sends 1Gbit/s. >> >> When that happens I see this alternating pattern of writing either to >> the 4 mvs disks, or writing to the Areca disks. >> But almost never are all disk accesses at the same time. >> And really never, never is there a mix of writing between the controller >> sets. > > Are all 8 disks in the same raidz vdev? Yes is a raidz1 with 8 disks. I know it is not optimal in performance, but I needed the amount of remaining diskspace. > Are you basing write activity on the drive LEDs? Yup. > > The Areca controller may be caching the writes in its battery-backed > cache and deferring the writes to when zfs tells it to flush its cache. > The other controller may be issuing the writes right away. This would > explain apparent 'split' writing behavior. Sounds like a fair assumption. Could remove the battery and see what happens then. The mvs device is relatively "simple" and has no significant memory on board. > There is even the possibilty that one of the controllers ignores the > cache flush request and performs the writes later when it feels like it. That would then be the Areca controller, bacause I have the feeling that it always writes later. --WjW