From mboxrd@z Thu Jan 1 00:00:00 1970 From: Douglas Gilbert Subject: Re: [RFC] aic94xx: attaching to the sas transport class Date: Mon, 06 Mar 2006 13:30:32 -0500 Message-ID: <440C7FC8.8050000@torque.net> References: <20060303101420.78398.qmail@web31806.mail.mud.yahoo.com> <1141399404.3928.5.camel@mulgrave.il.steeleye.com> <440867B7.70703@s5r6.in-berlin.de> Reply-To: dougg@torque.net Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Return-path: Received: from canuck.infradead.org ([205.233.218.70]:457 "EHLO canuck.infradead.org") by vger.kernel.org with ESMTP id S1752390AbWCFSbu (ORCPT ); Mon, 6 Mar 2006 13:31:50 -0500 In-Reply-To: <440867B7.70703@s5r6.in-berlin.de> Sender: linux-scsi-owner@vger.kernel.org List-Id: linux-scsi@vger.kernel.org To: Stefan Richter Cc: James Bottomley , ltuikov@yahoo.com, "Tarte, Robert" , linux-scsi Stefan Richter wrote: > James Bottomley wrote: > >>Assuming the cages are all powered up, which is beyond >>the driver control, then serialising the scan will allow one to >>specify /dev/sda1 deterministically for root. > > > Does SAS provide a persistent globally unique property of a device, or > has SAS to rely on bus topology to uniqely identify devices? That swings on what you mean by "device" but broadly: Yes to the first part, but ... SAS is a transport and SAS transport endpoints (i.e. "ports") have naa-5 world wide unique identifiers. That might sound great but most SAS disks are dual ported, so that gives two SAS (i.e. naa-5) addresses (typically consecutive). A dual ported SAS disk could/should have up to 4 naa-5 addresses: - one for SAS port 1 (primary) - one for SAS port 2 (secondary) - one for the target device - and, one for the logical unit A SAS (target) device might also be a bridge, for example, as found in SAS expanders that support SATA devices. SATA disks do not yet have mandated world wide unique addresses (but provision has been made for a naa-5 address). The SAS "port" address of a SATA disk is actually the bridge it is plugged into (but one could switch SATA disks). I suspect what you would really like to identify uniquely is the logical unit. Fuzziness remains due to the possibility of bridges. Doug Gilbert