From mboxrd@z Thu Jan 1 00:00:00 1970 From: Uma Krishnan Subject: Re: [PATCH 2/6] cxlflash: Fix to avoid virtual LUN failover failure Date: Thu, 17 Dec 2015 16:19:59 -0600 Message-ID: <5673350F.5040501@linux.vnet.ibm.com> References: <1449787867-23015-1-git-send-email-ukrishn@linux.vnet.ibm.com> <1449788029-23093-1-git-send-email-ukrishn@linux.vnet.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Return-path: Received: from e37.co.us.ibm.com ([32.97.110.158]:57619 "EHLO e37.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933927AbbLQWTt (ORCPT ); Thu, 17 Dec 2015 17:19:49 -0500 Received: from localhost by e37.co.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Thu, 17 Dec 2015 15:19:48 -0700 Received: from b03cxnp08025.gho.boulder.ibm.com (b03cxnp08025.gho.boulder.ibm.com [9.17.130.17]) by d03dlp02.boulder.ibm.com (Postfix) with ESMTP id CDEF23E40048 for ; Thu, 17 Dec 2015 15:19:46 -0700 (MST) Received: from d03av04.boulder.ibm.com (d03av04.boulder.ibm.com [9.17.195.170]) by b03cxnp08025.gho.boulder.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id tBHMJkBo30343208 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 tBHMJjZx031085 for ; Thu, 17 Dec 2015 15:19:46 -0700 In-Reply-To: <1449788029-23093-1-git-send-email-ukrishn@linux.vnet.ibm.com> Sender: linux-scsi-owner@vger.kernel.org List-Id: linux-scsi@vger.kernel.org To: linux-scsi@vger.kernel.org, James Bottomley , "Martin K. Petersen" , "Matthew R. Ochs" , "Manoj N. Kumar" , Brian King Cc: linuxppc-dev@lists.ozlabs.org, Ian Munsie , Andrew Donnellan 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