From owner-freebsd-scsi@FreeBSD.ORG Thu Mar 18 17:06:01 2010 Return-Path: Delivered-To: freebsd-scsi@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 75044106566B for ; Thu, 18 Mar 2010 17:06:01 +0000 (UTC) (envelope-from mj@feral.com) Received: from ns1.feral.com (ns1.feral.com [192.67.166.1]) by mx1.freebsd.org (Postfix) with ESMTP id 2EF4B8FC1C for ; Thu, 18 Mar 2010 17:06:00 +0000 (UTC) Received: from [192.168.221.2] (remotevpn [192.168.221.2]) by ns1.feral.com (8.14.3/8.14.3) with ESMTP id o2IH605N036357 (version=TLSv1/SSLv3 cipher=DHE-RSA-CAMELLIA256-SHA bits=256 verify=NO) for ; Thu, 18 Mar 2010 09:06:00 -0800 (PST) (envelope-from mj@feral.com) Message-ID: <4BA25D78.2090907@feral.com> Date: Thu, 18 Mar 2010 10:06:00 -0700 From: Matthew Jacob Organization: Feral Software User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.8) Gecko/20100301 Fedora/3.0.3-1.fc11 Thunderbird/3.0.3 MIME-Version: 1.0 To: freebsd-scsi@freebsd.org References: <20100318154138.GA30096@orion.hsd1.pa.comcast.net> In-Reply-To: <20100318154138.GA30096@orion.hsd1.pa.comcast.net> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit X-Greylist: Sender DNS name whitelisted, not delayed by milter-greylist-4.2.3 (ns1.feral.com [192.168.221.1]); Thu, 18 Mar 2010 09:06:00 -0800 (PST) Subject: Re: Optimum dev_openings value X-BeenThere: freebsd-scsi@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list Reply-To: mj@feral.com List-Id: SCSI subsystem List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 18 Mar 2010 17:06:01 -0000 Openings changes reflect when and how a device sends back a QUEUE FULL message, which causes FreeBSD to adjust the openings. That is disk, access pattern, and timing dependent. There are a number of theories about whether the 'openings' value should be bumped back up after having been throttled down. Nobody can agree on these theories, so the openings stay where they are. You might try manually adjusting them up on a periodic basis. > Hi, > > I have three machines running 8.0-RELEASE, each with two mirrored Seagate > SCSI disks using ZFS. In making sure these machines are performing as > best as possible, I'm trying to find what the best practices are with > regards to dev_openings values, and what determines the default > dev_openings value. > > Two machines have identical ahc(4) Adaptec AIC7899 Ultra160 SCSI adapters, > but display different defaults, which I have not had luck finding an > explanation: > > h04# camcontrol tags da0 -v > (pass0:ahc1:0:0:0): dev_openings 33 > (pass0:ahc1:0:0:0): dev_active 0 > (pass0:ahc1:0:0:0): devq_openings 33 > (pass0:ahc1:0:0:0): devq_queued 0 > (pass0:ahc1:0:0:0): held 0 > (pass0:ahc1:0:0:0): mintags 2 > (pass0:ahc1:0:0:0): maxtags 255 > > h21# camcontrol tags da0 -v > (pass0:ahc0:0:0:0): dev_openings 64 > (pass0:ahc0:0:0:0): dev_active 0 > (pass0:ahc0:0:0:0): devq_openings 64 > (pass0:ahc0:0:0:0): devq_queued 0 > (pass0:ahc0:0:0:0): held 0 > (pass0:ahc0:0:0:0): mintags 2 > (pass0:ahc0:0:0:0): maxtags 255 > > h04# camcontrol devlist > at scbus1 target 0 lun 0 (pass0,da0) > at scbus1 target 1 lun 0 (pass1,da1) > > h21# camcontrol devlist > at scbus0 target 0 lun 0 (pass0,da0) > at scbus0 target 1 lun 0 (pass1,da1) > > Is there an obvious explanation for the difference here? > > The third machine uses sym(4), which I expect would cause a different > default dev_openings (currently defaulted to 44). > > Is there a general rule to adjusting this value? > >