Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933040AbZGPSoI (ORCPT ); Thu, 16 Jul 2009 14:44:08 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S932941AbZGPSoH (ORCPT ); Thu, 16 Jul 2009 14:44:07 -0400 Received: from mail.lang.hm ([64.81.33.126]:37131 "EHLO bifrost.lang.hm" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932920AbZGPSoH (ORCPT ); Thu, 16 Jul 2009 14:44:07 -0400 Date: Thu, 16 Jul 2009 11:43:55 -0700 (PDT) From: david@lang.hm X-X-Sender: dlang@asgard To: James Smart cc: Boaz Harrosh , linux-kernel , "linux-scsi@vger.kernel.org" Subject: Re: deterministic scsi order with async scan In-Reply-To: <4A5F723B.7070408@emulex.com> Message-ID: References: <4A5F100E.9000107@panasas.com> <4A5F723B.7070408@emulex.com> User-Agent: Alpine 1.10 (DEB 962 2008-03-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2560 Lines: 54 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? David Lang >> I am building a system that will have two drives in a hardware mirror on >> one SCSI card, and 160 drives on a FC (SCSI) card. why should my boot have >> to go and examine all 162 drives to look for an ID on every partition just > Because its the only safe way to ensure proper device identification. > > -- james s > -- 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/