From mboxrd@z Thu Jan 1 00:00:00 1970 From: James Bottomley Subject: Re: [PATCH RFC 2/2] implement transport scan callout for iscsi Date: Wed, 25 May 2005 14:04:07 -0400 Message-ID: <1117044247.5210.15.camel@mulgrave> References: <42936441.0b798bab.39a4.ffff9774SMTPIN_ADDED@mx.googlegroups.com> <42939610.3070104@cs.wisc.edu> <1116976678.7710.34.camel@mulgrave> <000b01c560c0$42c59700$03031eac@ivivity.com> <1116982816.7710.58.camel@mulgrave> <4294972D.4030807@adaptec.com> Mime-Version: 1.0 Content-Type: text/plain Content-Transfer-Encoding: 7bit Return-path: Received: from stat16.steeleye.com ([209.192.50.48]:47852 "EHLO hancock.sc.steeleye.com") by vger.kernel.org with ESMTP id S261889AbVEYSEZ (ORCPT ); Wed, 25 May 2005 14:04:25 -0400 In-Reply-To: <4294972D.4030807@adaptec.com> Sender: linux-scsi-owner@vger.kernel.org List-Id: linux-scsi@vger.kernel.org To: Luben Tuikov Cc: open_iscsi , open-iscsi@googlegroups.com, Mike Christie , 'SCSI Mailing List' On Wed, 2005-05-25 at 11:18 -0400, Luben Tuikov wrote: > MC/S in iSCSI can be seen as a "wide port" in SAS. > > That is, commands are ordered, nexus is the same, going to the same port, > etc, etc, etc. MC/S, has nothing to do with multipathing, which sits above > the nexus level. With MC/S the nexus is the same. When I use the term "multi-pathing" I mean multiple virtual paths may be traversed to get a command from an application to a target device. Under that definition, dm-multipath, MC/S and even network bonding are all examples of multi-pathing. The visibility of the coding is what I have an issue with. bonding could be inherited invisibly from the network but MC/S has to be explicitly coded in the software initiator whereas dm-multipath is done above the driver: one code base for all multi-path implementations. > MC/S is a good thing. a) It's optional, so you can't rely on it. b) it requires explicit coding in the driver which is a big negative since you can't leverage our existing multi-path code (i.e. more bug prone) c) The feature set it provides to Linux is identical to the feature set that dm-multipath provides. It's pointless to add support for an optional feature that provides no additional benefit (and its detrimental when the only addition is a potential negative impact to the code quality). James