Re: Question about MOUNT in multiple clusters

From: Jeff Cameron (roktsci_at_comcast.net)
Date: 06/14/05 

Date: Mon, 13 Jun 2005 16:53:49 -0700

On 6/13/05 10:26 AM, in article 42ADC1A9.F3F0E61A@teksavvy.com, "JF Mezei"
<jfmezei.spamnot@teksavvy.com> wrote:

> One of the patches for VAX VMS 7.3 has the following text:
>
> o A MOUNT/NOWRITE command on a disk on one cluster will now
> work correctly even if the disk is mounted with a /WRITE
> qualifier on another cluster in the SAN (Storage Area
> Network). Previously, depending on the order in which the
> mounts were executed, the mount would fail with the error
> message:
>
>
>
> I would have understood if the 3rd line had been "qualifier on another
> node in the cluster".
>
> But this implies that that seperate clusters despite not having DLM
> between each other, will still know about how the other cluster has
> mounted disks ? (or that it would have mounted it). How is that
> accomplished ?
>
> Does the SAN software in the SAN and on VMS provide extra-cluster
> resource database that allow any independant system attached to the SAN
> (a cluster being an independant system) to know about all the disk
> resources being accessed by the others connected to the SAN ?
In a SAN environment you can have many cluster mount LUNs with NOWRITE
access, and only one with WRITE access. However in a NAS environment
multiple nodes (clusters) can mount a resource with simultaneous write
access. This is because NAS is akin to NFS mounting where you are mounting a
file server rather than SAN which is a a block server.

The message above does not imply multiple cluster write access to a LUN but
only says that the order of the mounts is not important.

Unless of course there is some sort of Hook in VMS SAN technology that would
allow multiple Distributed lock managers in separate clusters to
communicate, of which I am unaware.

Jeff Cameron

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