[dm-devel] Re: Is there a grand plan for FC failover?

[Mike Anderson <andmike us ibm com>]

Smart, James [James Smart Emulex com] wrote:
> 
> 
> > -----Original Message-----
> > From: James Bottomley [mailto:James Bottomley SteelEye com]
> > 
> > On Thu, 2004-01-29 at 09:49, Philip R. Auld wrote:
> > > It needs to be known to the pathing layer if you've got 
> > load balancing. 
> > > It has to know which path has the reservation and only use that one.
> > 
> > Well, yes, but your multiple active path implementation just collapsed
> > back down to single path in the face of reservations, so it would
> > probably be better simply to use failover in the face of reservations
> > and clustering.
> 
> Why do you imply that you're down to a single path ? With multiple port
> devices, and the T10 unclarity on multiport support, simple reservations
> didn't bring you down to the single port access you are describing. Some
> devices may have implemented it this way, but the standard didn't say they
> had to or even that they should.
> 
> And this picture changes significantly with the use of Persistent
> Reservations and the use of keys.
> 

It appears you are mixing port and path. If you have multiple paths to a
port created by multiple adapters connecting to this port through a bus,
fabric, etc. then simple reservations should restrict you to only one
path to this port. Is there a device that implements simple reservations
and allows multiple initiators access?

-andmike
--
Michael Anderson
andmike us ibm com