From mboxrd@z Thu Jan 1 00:00:00 1970 From: Hannes Reinecke Subject: Re: Powerpath vs dm-multipath - two points of FUD? Date: Mon, 15 Sep 2014 08:54:17 +0200 Message-ID: <54168D19.3010908@suse.de> References: <454E18A46D7B064CA63B41E99AD179508A754100@MX103CL02.corp.emc.com> Reply-To: device-mapper development Mime-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Return-path: In-Reply-To: <454E18A46D7B064CA63B41E99AD179508A754100@MX103CL02.corp.emc.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: device-mapper development List-Id: dm-devel.ids Hi Jerome, On 09/14/2014 08:44 PM, Levy, Jerome wrote: >> Firstly, apologies if this is a common topic and my intentions are not = >> to start a flame war. I've googled extensively but haven't found >> specific information to address my queries, so I thought I would turn he= re. > = > At the risk of getting involved in a religious discussion (disclaimer: I = am an EMC employee > and was an advanced support engineer for both PowerPath and dm-multipath) I thought I'd pass > along a few thoughts that might help: > = > PowerPath costs money. dm-multipath is included with the OS distro. > = [ .. ] > = > PowerPath contains proprietary load sensing and balancing algorithms whic= h may help performance > in a given situation. (It does. I've seen them.) YMMV. > = Unfortunately I'll have to agree with Jerome here. If you have in-depth knowledge of the array you can cut some corners and optimize for certain scenarios. We haven't, and so we can't. Neither can we estimate how _likely_ such a scenario is; We live on the assumption that it's not, and that most customers are happily living with the standard setups. Surprisingly enough, most do :-) > Request size and other switching options can be useful in a number > of specific situations -- some may call them corner cases, but streaming > media, heavy database backups, large dataset transfers, and others have > been shown to benefit from alternate PowerPath policies. > = See above. Of course. > As Hannes points out, PowerPath is supported by EMC. If things don't work, > you have someone to call. That can be comforting in the middle of the night :) > = But so is device-mapper multipath :-) Sorry. > I've seen both PowerPath and native multipath solutions provide a lot of > value in different ways, and the decision as to which to use is not always > clear-cut. Hope this helps! > = Thanks for that. It surely helps. Cheers, Hannes -- = Dr. Hannes Reinecke zSeries & Storage hare@suse.de +49 911 74053 688 SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 N=FCrnberg GF: J. Hawn, J. Guild, F. Imend=F6rffer, HRB 16746 (AG N=FCrnberg)