Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933158AbZGPTsP (ORCPT ); Thu, 16 Jul 2009 15:48:15 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S933112AbZGPTsO (ORCPT ); Thu, 16 Jul 2009 15:48:14 -0400 Received: from mail.lang.hm ([64.81.33.126]:40672 "EHLO bifrost.lang.hm" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932952AbZGPTsN (ORCPT ); Thu, 16 Jul 2009 15:48:13 -0400 Date: Thu, 16 Jul 2009 12:48:06 -0700 (PDT) From: david@lang.hm X-X-Sender: dlang@asgard To: James Bottomley cc: James Smart , Boaz Harrosh , linux-kernel , "linux-scsi@vger.kernel.org" Subject: Re: deterministic scsi order with async scan In-Reply-To: <1247773155.6606.265.camel@mulgrave.site> Message-ID: References: <4A5F100E.9000107@panasas.com> <4A5F723B.7070408@emulex.com> <1247773155.6606.265.camel@mulgrave.site> User-Agent: Alpine 1.10 (DEB 962 2008-03-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; format=flowed; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2845 Lines: 58 On Thu, 16 Jul 2009, James Bottomley wrote: > On Thu, 2009-07-16 at 11:43 -0700, david@lang.hm wrote: >> On Thu, 16 Jul 2009, James Smart wrote: >> >>> david@lang.hm wrote: >>>> On Thu, 16 Jul 2009, Boaz Harrosh wrote: >>>> >>>> >>>>> It is highly discouraged to setup any kind of system that depends >>>>> on device-names for block-devices. mounts have the mount by-label >>>>> or mount by-uuid. Any other subsystem should go by /dev/disk/by-id/* >>>>> slinks to find a persistent raw block-device. the id is generated >>>>> from characteristics inside the disk itself so it will be the same >>>>> no matter what host connection or bus it is connected too (almost). >>>>> >>>>> This is because even if the boot order is consistent, the device-name >>>>> is so volatile in the life-span of a system. Did I boot with a removable >>>>> USB inserted. that camera or printer was on or off, disk was connected >>>>> to the other port. Any such change will break things and give you a very >>>>> poor user experience. >>>>> >>>> >>>> for a laptop you areprobably correct, but for a server or embedded system >>>> that doesn't have it's hardware changing all the time you are not correct. >>>> >>>> especially on a system with lots of drives, why should I have to create an >>>> initrd that goes and searches dozens or hundreds of drives to find out >>>> which one to boot from? >>>> >>> Boaz is correct. Many enterprise SCSI subsystems (FC, SAS) do not have hard >>> transport addresses for each device like Parallel SCSI used to. Thus, any >>> difference in order of appearance of the devices (power-up ordering, FC ALPA >>> assignment based on who's loop master, order that switch reports them, is an >>> array in a failover mode with 1 controller non-existent), or if LUN >>> configuration on an array changes, or as a drive may fail (especially with >>> hundreds), there's no guarantee you will see the same thing in the same order >>> w/o name binding. Same thing is true if one of those adapters fails or is >>> swapped out. >> >> yes, but does your system change the order of your internal direct >> attached drives with your FC/SAN drives? > > Certainly, it can. The way BIOS booting gets around this is either to > use some type of physical indicator (like phy number for SAS) to find C: > or to use a persistent ID mapping scheme (which is pretty much > equivalent to our /dev/disk/by-id/ udev one). so if I don't use udev but do want the async detection my only option to have it boot from card 1 instead of card 2 is to just keep rebooting the machine until it guesses right? David Lang -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/