From:	MERC::"uunet!WKUVX1.BITNET!MacroMan" 29-MAR-1993 14:44:04.56
To:	MACRO32@WKUVX1.BITNET
CC:	
Subj:	Re: SHOW DEVICE and mounted status.

In article <1993Mar28.144910.1367@dmc.com>, munroe@dmc.com (Dick Munroe)
writes...
>How does SHOW DEVICE get its information about the device being
>mounted?  I have a cluster, a disk mounted on one node, but not
>cluster wide.  Mount counts are what you would expect, 0 on all
>nodes except the one having the mounted device.  The unexpected
>thing is that the DEVCHAR bit indicating mounted is clear on all
>nodes except the one having the mounted device (according to
>F$GETDVI).  The reason it's unexpected is because SHOW
>DEVICE/FULL show that the device IS mounted on all other nodes on
>the cluster.
>
>So how does SHOW DEVICE get the mounted information?  By looking
>at the UCBs directly?

Currently, OpenVMS does not provide a documented mechanism to obtain device
information such as the mount count for a device across the VAXcluster.
However, this information is accessible for each device available to the
VAXcluster by reading information in the Device Allocation Lock (DAL)
resource for a device.

The DAL resource serializes access to device/mount context for a device
available to nodes in a VAXcluster.  The DAL for a device is accessed using
the OpenVMS Distributed Lock Manager system services Enqueue Lock Request
(SYS$ENQ), Get Lock Information (SYS$GETLKI), and Dequeue Lock Request
(SYS$DEQ).

This topic is discussed in detail in the May/June 1992 issue of VAX
Professional in an article titled: Obtaining Device/Mount context for
Cluster Device written by Eric M. LaFranchi.

If you would like a copy of my program that dumps the device allocation
lock information, please feel free to request it of me by email.

-- Eric

==============================================================================
Eric M. LaFranchi       Phone: (510) 748 - 2919
                        Email: eml@ingres.com
                        Email: eric%emlsoft@netcom.com