From mboxrd@z Thu Jan 1 00:00:00 1970 From: Douglas Gilbert Subject: Re: sg driver and Fedora Core 2 Date: Mon, 07 Jun 2004 18:56:48 +1000 Sender: linux-scsi-owner@vger.kernel.org Message-ID: <40C42DD0.2020003@torque.net> References: <40B74725.90403@torque.net> <20040528172535.GD13961@devserv.devel.redhat.com> <1085846125.2101.29.camel@mulgrave> <20040529155744.GA32621@devserv.devel.redhat.com> <1085846840.2103.47.camel@mulgrave> <20040529162912.GA5922@devserv.devel.redhat.com> <1085849399.2004.101.camel@mulgrave> <40B8C81E.3050106@pobox.com> <20040529172916.GD18613@suse.de> <40B9B95A.40304@torque.net> <20040530104145.GA3172@devserv.devel.redhat.com> Reply-To: dougg@torque.net Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Return-path: Received: from bunyip.cc.uq.edu.au ([130.102.2.1]:58638 "EHLO bunyip.cc.uq.edu.au") by vger.kernel.org with ESMTP id S264330AbUFGI5H (ORCPT ); Mon, 7 Jun 2004 04:57:07 -0400 In-Reply-To: <20040530104145.GA3172@devserv.devel.redhat.com> List-Id: linux-scsi@vger.kernel.org To: Alan Cox Cc: SCSI Mailing List Alan Cox wrote: > On Sun, May 30, 2004 at 08:37:14PM +1000, Douglas Gilbert wrote: > >>configuring the SAS domain. Expanders are SAS devices but >>not SCSI devices (i.e. they are neither initiators nor >>targets ***). It seems obvious that the management of a SAS >>domain should be done from the user space. Only those >>expanders and devices directly attached to a SAS Host Bus >>Adapter should automatically be visible. > > > Is there any reason that the SAS domain should in itself be a character > device file. I've always thought of it as a network and anticipated > a network layer interface for such things. That might just be my background > however. Alan, In the SCSI parallel world the "domain" is usually called the "bus" which is a set of targets and one or more initiators and the ribbon (or external) cable that interconnect them. In SAS the "domain" is a little more rubbery. After wide links are taken into account, there cannot be multiple paths between scsi devices within one SAS domain (i.e. "no loops"). An expander is part of the service interconnect subsystem of a _single_ SAS domain (i.e. it can't be shared). This means that expanders can be wired incorrectly. Even simple interconnects need some thought: | SAS 2 | | port HBA | -------------- | | | | | | | | ------------- | SAS dual | |ported disk| Is this a (2 phy) wide-link, single SAS domain or two SAS domains? On current indications it is two SAS domains since dual ported SAS disks have different SAS addresses on each port. [The fact that the SAS HBA has the same SAS addresses on both phys only meets half the requirement for a wide link.] See SAS Quiz question 1 (then its answer) in the pdfs at: http://www.scsita.org/aboutscsi/sas/tutorials.html for a more complex scenario. Detecting and explaining to a user why his/her SAS domain(s) is incorrectly wired will be an interesting challenge. So it wasn't the SCSI domain that I was proposing should be a char (or network) device file. It was the SMP target port inside each expander that is used for discovery, configuration and statistics that needs a packet based initiator driver/interface (like the sg driver). The concept of a SAS domain I would rather leave for a user space program. Doug Gilbert