From mboxrd@z Thu Jan 1 00:00:00 1970 From: James Bottomley Subject: RE: Is there a grand plan for FC failover? Date: 29 Jan 2004 13:31:20 -0500 Sender: linux-scsi-owner@vger.kernel.org Message-ID: <1075401081.2426.98.camel@mulgrave> References: <3356669BBE90C448AD4645C843E2BF2802C013BE@xbl.ma.emulex.com> Mime-Version: 1.0 Content-Type: text/plain Content-Transfer-Encoding: 7bit Return-path: Received: from stat1.steeleye.com ([65.114.3.130]:29902 "EHLO hancock.sc.steeleye.com") by vger.kernel.org with ESMTP id S266319AbUA2Sbd (ORCPT ); Thu, 29 Jan 2004 13:31:33 -0500 In-Reply-To: <3356669BBE90C448AD4645C843E2BF2802C013BE@xbl.ma.emulex.com> List-Id: linux-scsi@vger.kernel.org To: "Smart, James" Cc: "Philip R. Auld" , 'Patrick Mansfield' , Simon Kelley , SCSI Mailing List , dm-devel@sistina.com On Thu, 2004-01-29 at 12:35, Smart, James wrote: > Why do you imply that you're down to a single path ? With multiple port > devices, and the T10 unclarity on multiport support, simple reservations > didn't bring you down to the single port access you are describing. Some > devices may have implemented it this way, but the standard didn't say they > had to or even that they should. T10 implies SCSI-2 reservations protect single paths. Any multi-port SCSI-2 reservation implementations tend to be vendor specific. That's a nasty I don't think we want to get into. > And this picture changes significantly with the use of Persistent > Reservations and the use of keys. That's the point, it doesn't. T10 clarified the persistent reservation holder (5.6.2.6 in rev 16) so that it's a specific I_T nexus (which is effectively a specific path unless you have fabric redundancy) except for all registrant reservations (which aren't useful for clustering). Obviously, this seems to require that the reservation be held against everyone when the port switches, which would preclude doing user level reservation handling, hence the need for a separate ownership API (assuming all vendors get on the same page about this). James