From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jeff Garzik Subject: Re: generating a Linux WWN? Date: Thu, 27 Sep 2007 10:19:23 -0400 Message-ID: <46FBBBEB.4020605@garzik.org> References: <46FB8024.8040807@garzik.org> <46FBB86B.8000206@emulex.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: Received: from srv5.dvmed.net ([207.36.208.214]:53649 "EHLO mail.dvmed.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750918AbXI0OT0 (ORCPT ); Thu, 27 Sep 2007 10:19:26 -0400 In-Reply-To: <46FBB86B.8000206@emulex.com> Sender: linux-scsi-owner@vger.kernel.org List-Id: linux-scsi@vger.kernel.org To: James.Smart@Emulex.Com Cc: linux-scsi James Smart wrote: > Uh, although this may work very well for small constrained configs, as one > who debugs larger environments (and things always grow or get connected in > ways you don't expect), depending on a random number for uniqueness makes > me very unsettled. Debugging that small-percentage potential, when/if it > does occur can be an absolute nightmare with all kinds of weird behavior. > Rarely will you solve it from the context of a single server. There are > lots of ways to cheat, but I believe they all have to be based on some > small part that is guaranteed to be unique (like the IEEE id's). That's the ideal world, sure :) But the reality is, just like with ethernet MAC addresses, you don't always have one when you "supposed to" have one. There are obvious limitations and problems arising from a generated WWN -- particularly for an HBA, where serial numbers and other unique identifiers are scarce. But that doesn't wish the missing-WWN problem away. Decades of networking experience have taught us a few things :) As an aside, we also need a way to override the HBA's WWN, just like we do with ethernet MAC address. Jeff