Subject: Re: System unique identifier.....
To: None <>
From: Matthew Jacob <>
List: tech-kern
Date: 06/25/1999 10:34:46
> On Thu, 24 Jun 1999, Matthew Jacob wrote:
> > Specifically in this case a Node WWN for fibre channel fabrics that does
> > not depend upon an assigned WWN in any particular Fibre Channel card
> > (multipathing might make it desirable to have a synthetic Node WWN that
> > can also be passed to partner systems in  a failover configuration).
> Matt,
> We've been hashing this issue out quite a bit.  Since a Fibre Channel card

I thought you might be!

> is by definition a fibre channel controller, each card should have a
> unique WWN that is used for the node WWN.  If you swap a controller, the
> node WWN should change.

Really?  Couldn't the Port WWN change and the Node WWN stay constant? I
mean, yes, for FC controllers that have WWN in the 0x2XXXXXXXXXXXX range,
the Node WWN is 0x20... and the Port is 0x22... but it seems like this is
a soft relationship- you *could* have Port && Node unique for each card,
but then that requires all fabric clients to know (via some other
arbitrary mechanism) that distinct WWNs are really the same 'box'.

What's the Leadville group's opinion on this?

> The concept is that for SCSI disks and RAID boxen at least, the unique
> identifier is the LUN WWN, which is the unique label for the data
> contained on that LUN.  The LUN WWN is 128 bits wide is generated from a
> combination of the controller's node WWN and a timestamp, and is lost when
> the LUN is destroyed.

Sure. That's reasonable enough, but not necessarily a problem that needs
solving. The LUN isn't interesting in that what you want a known Node WWN
for (routed to via multiple Port WWNs) so that when you construct the
addressing to some physical box you, and intervening FC switches, can get
the frame there. Beyond that, multilevel LUN numbers seem adequate for
*within box* addressing, and then whatever volume management software
needs to look at 

> If you're not dealing with SCSI disks, well, I don't know if the standards
> guys have considered that sort of situation yet.  

Yes indeed.

At any rate, the WWN issue is just one use of this identifier.