RE: Summary of the Multi-Path BOF at OLS and future directions

jansen, frank
2003-08-08T12:13:19Z

>
> Christoph Hellwig wrote:
>
> > > 4. Configuration of this solution would be extremely
> important. The
> > > idea here is to rely on the udev solution currently
> making its way into
> > > the kernel and essentially have a vendor specific multi-path
> > > configuration as a udev plug-in.
> > >
> > > 5. Vendor value add for specific devices could be encoded both as
> > > configuration (udev) pieces and plug-ins to the upper
> layer multi-path
> > > driver to activate any proprietary vendor specific
> configuration options
> > > that may be needed for specific solutions.
> >
> > What are examples of such value add?
>
> Some older EMC RAID boxes need a special "TRESPASS" command
> (implemented
> as a MODE SELECT) to switch the ownership of a LUN from one path
> ("Storage Processor") to the other. The newer ones do this
> automatically, though.

The delineation between the EMC boxes that require vs. not require
a "TRESPASS" command lies not with their age, but rather their family.
The CLARiiON family of Storage Arrays require a "TRESPASS" command to
move a LUN from one redundant Storage Processor (SP) to another. On the
other hand, Symmetrix Storage Arrays do not use any such behavior. In
a nutshell, the Symmetrix is active on all paths, on which the LUN is
presented, whereas the CLARiiON is active on one SP and passive on the
other SP.

> Without the TRESPASS, you'd see the LUN (INQUIRY), but you can't do
> anything with it, even a simple READ CAPACITY fails.

This is correct. Note, that it is not necessarily desirable to TRESPASS
the LUN, as there may be an active path from the other SP to this or
another HBA on the host system.

> --
> Josef Möllers (Pinguinpfleger bei FSC)
> If failure had no penalty success would not be a prize
> -- T. Pratchett
> -
> To unsubscribe from this list: send the line "unsubscribe
> linux-scsi" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at http://vger.kernel.org/majordomo-info.html
>
-
To unsubscribe from this list: send the line "unsubscribe linux-scsi" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html