From mboxrd@z Thu Jan 1 00:00:00 1970 From: Hannes Reinecke Subject: Re: [PATCH v2] dm pref-path: provides preferred path load balance policy Date: Fri, 22 Jan 2016 14:42:32 +0100 Message-ID: <56A231C8.90602@suse.de> References: <1453469502-15606-1-git-send-email-ravikanth.nalla@hpe.com> Reply-To: device-mapper development Mime-Version: 1.0 Content-Type: text/plain; charset="windows-1252" Content-Transfer-Encoding: quoted-printable Return-path: In-Reply-To: <1453469502-15606-1-git-send-email-ravikanth.nalla@hpe.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: dm-devel-bounces@redhat.com Errors-To: dm-devel-bounces@redhat.com To: dm-devel@redhat.com List-Id: dm-devel.ids On 01/22/2016 02:31 PM, Ravikanth Nalla wrote: > v2: > - changes merged with latest mainline and functionality re-verified. > - performed additional tests to illustrate performance benefits of > using this feature in certain configuration. > = > In a dm multipath environment, providing end user with an option of > selecting preferred path for an I/O in the SAN based on path speed, > health status and user preference is found to be useful. This allows > a user to select a reliable path over flakey/bad paths thereby > achieving higher I/O success rate. The specific scenario in which > it is found to be useful is where a user has a need to eliminate > the paths experiencing frequent I/O errors due to SAN failures and > use the best performing path for I/O whenever it is available. > = > Another scenario where it is found to be useful is in providing > option for user to select a high speed path (say 16GB/8GB FC) > over alternative low speed paths (4GB/2GB FC). > = > A new dm path selector kernel loadable module named "dm_pref_path" > is introduced to handle preferred path load balance policy > (pref-path) operations. The key operations of this policy is to > select and return user specified path from the current discovered > online/ healthy paths. If the user specified path do not exist in > the online/ healthy paths list due to path being currently in > failed state or user has mentioned wrong device information, it > will fall back to round-robin policy, where all the online/ healthy > paths are given equal preference. > = > Functionality provided in this module is verified on wide variety > of servers ( with 2 CPU sockets, 4 CPU sockets and 8 CPU sockets). > Additionally in some specific multipathing configurations involving > varied path speeds, proposed preferred path policy provided some > performance improvements over existing round-robin and service-time > load balance policies. > = Shouldn't service-time provide similar functionality? After all, for all scenarios described above the preferred path would have a lower service time, so they should be selected automatically, no? Cheers, Hannes -- = Dr. Hannes Reinecke Teamlead Storage & Networking hare@suse.de +49 911 74053 688 SUSE LINUX GmbH, Maxfeldstr. 5, 90409 N=FCrnberg GF: F. Imend=F6rffer, J. Smithard, J. Guild, D. Upmanyu, G. Norton HRB 21284 (AG N=FCrnberg)