From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from e36.co.us.ibm.com (e36.co.us.ibm.com [32.97.110.154]) (using TLSv1 with cipher CAMELLIA256-SHA (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id D4E921A119C for ; Fri, 18 Dec 2015 09:19:49 +1100 (AEDT) Received: from localhost by e36.co.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Thu, 17 Dec 2015 15:19:47 -0700 Received: from b03cxnp08027.gho.boulder.ibm.com (b03cxnp08027.gho.boulder.ibm.com [9.17.130.19]) by d03dlp03.boulder.ibm.com (Postfix) with ESMTP id 03CDF19D8026 for ; Thu, 17 Dec 2015 15:07:51 -0700 (MST) Received: from d03av04.boulder.ibm.com (d03av04.boulder.ibm.com [9.17.195.170]) by b03cxnp08027.gho.boulder.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id tBHMJkCw23462104 for ; Thu, 17 Dec 2015 15:19:46 -0700 Received: from d03av04.boulder.ibm.com (loopback [127.0.0.1]) by d03av04.boulder.ibm.com (8.14.4/8.14.4/NCO v10.0 AVout) with ESMTP id tBHMJjZt031085 for ; Thu, 17 Dec 2015 15:19:46 -0700 Subject: Re: [PATCH 2/6] cxlflash: Fix to avoid virtual LUN failover failure To: linux-scsi@vger.kernel.org, James Bottomley , "Martin K. Petersen" , "Matthew R. Ochs" , "Manoj N. Kumar" , Brian King References: <1449787867-23015-1-git-send-email-ukrishn@linux.vnet.ibm.com> <1449788029-23093-1-git-send-email-ukrishn@linux.vnet.ibm.com> Cc: linuxppc-dev@lists.ozlabs.org, Ian Munsie , Andrew Donnellan From: Uma Krishnan Message-ID: <5673350F.5040501@linux.vnet.ibm.com> Date: Thu, 17 Dec 2015 16:19:59 -0600 MIME-Version: 1.0 In-Reply-To: <1449788029-23093-1-git-send-email-ukrishn@linux.vnet.ibm.com> Content-Type: text/plain; charset=windows-1252; format=flowed List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On 12/10/2015 4:53 PM, Uma Krishnan wrote: > From: "Matthew R. Ochs" > > Applications which use virtual LUN's that are backed by a physical LUN > over both adapter ports may experience an I/O failure in the event of > a link loss (e.g. cable pull). > > Virtual LUNs may be accessed through one or both ports of the adapter. > This access is encoded in the translation entries that comprise the > virtual LUN and used by the AFU for load-balancing I/O and handling > failover scenarios. In a link loss scenario, even though the AFU is > able to maintain connectivity to the LUN, it is up to the application > to retry the failed I/O. When applications are unaware of the virtual > LUN's underlying topology, they are unable to make a sound decision of > when to retry an I/O and therefore are forced to make their reaction to > a failed I/O absolute. The result is either a failure to retry I/O or > increased latency for scenarios where a retry is pointless. > > To remedy this scenario, provide feedback back to the application on > virtual LUN creation as to which ports the LUN may be accessed. LUN's > spanning both ports are candidates for a retry in a presence of an I/O > failure. > > Signed-off-by: Matthew R. Ochs > --- Reviewed-by: Uma Krishnan