You
can remove shadow set members and dissolve shadow sets with the
DCL command DISMOUNT. You must have GRPNAM and SYSNAM user privileges
to dismount group and system volumes. You must also have the LOG_IO
user privilege to use the /POLICY=[NO]MINICOPY [=OPTIONAL] qualifier).
The DISMOUNT command has the following format: DISMOUNT {device-name[:] virtual-unit-name}
The action taken differs depending on whether you specify
an individual shadow set member or the shadow set (by its virtual
unit name) on the DISMOUNT command:
If you specify the device name of
a shadow set member, only that member is dismounted, and the remaining
shadow set members continue servicing I/O requests.
If you specify a shadow set virtual unit, all shadow
set members are dismounted and the shadow set is dissolved.
To dismount a shadow set that is mounted across an OpenVMS
Cluster system, include the /CLUSTER qualifier with the DISMOUNT
command. If you dismount a shadow set without including the /CLUSTER qualifier,
only the node from which you issued the command dismounts the shadow
set. The shadow set remains operational on the other OpenVMS Cluster
nodes that have the shadow set mounted.
If the disks on your system are neither SCSI nor Fibre Channel
disks, you can use the /NOUNLOAD qualifier on the DISMOUNT command
to prevent the disk volume or volumes from spinning down. The devices
remain in a ready state. If you specify the /UNLOAD qualifier when
dismounting a virtual unit, the disk volumes are physically spun
down after the shadow set is dissolved. See
the HP OpenVMS DCL Dictionary for more information about using the DISMOUNT command
and its qualifiers.
Removing Members from Shadow Sets To remove an individual member from a shadow set, specify
the name of the physical device with the DISMOUNT command. For example:
$ DISMOUNT $5$DUA7:
When you dismount an individual shadow set member, all outstanding
I/O operations are completed and the member is removed from the
set.
Starting with OpenVMS Alpha Version 7.3, the /FORCE_REMOVAL ddcu: qualifier
is available. If connectivity to a device has been lost and the
shadow set is in mount verification, /FORCE_REMOVAL ddcu: can be used to immediately expel a named
shadow set member (ddcu: ) from the shadow set. If you omit this qualifier,
the device is not dismounted until mount verification completes.
Note that this qualifier cannot be used in conjunction with the
/POLICY=[NO]MINICOPY [=OPTIONAL] qualifier.
The device specified must be a member of a shadow set that
is mounted on the node where the command is issued.
The /FORCE_REMOVAL qualifier gives system managers greater
control of shadow sets whose members are located at different sites
in an OpenVMS Cluster configuration. SET DEVICE and SET SHADOW command qualifiers
are also available for specifying disaster-tolerant management attributes
for shadow set members, as described in
Specifying Disaster-Tolerant Management Attributes (Alpha Only) and in
Managing Copy and Merge Operations (Alpha Only).
You cannot dismount a device if it is the only source
member in a shadow set. All shadow sets must have at least one valid
source member. If you try to dismount the only source member device,
the DISMOUNT command fails and returns the message:
%DISM-F-SRCMEM, Only source member of shadow set cannot be dismounted
The only way to dismount the last source member of a shadow
set is to dissolve the shadow set by specifying the virtual unit
name on the DISMOUNT command.
Dissolving Shadow Sets The way you dissolve
a shadow set depends on whether it is mounted on a single system
or on two or more systems in an OpenVMS Cluster system. In both
cases, you use the DISMOUNT command. If the shadow set is mounted
on a single system, you will dissolve the shadow set by specifying
its virtual unit name with the DISMOUNT command. If the shadow set
is mounted in a cluster, you must include the /CLUSTER qualifier to
dissolve the DSA36 shadow set across the cluster. For example:
$ DISMOUNT /CLUSTER DSA36:
Dismounting the shadow set can be done only after all files
are closed, thereby ensuring that the dismounted disks are fully
consistent from a file system perspective. The dismount operation
marks the shadow set members as being properly dismounted so that
a rebuild is not required the next time the disks are mounted. However,
if a merge operation was either pending or in progress, then the
dismount operation marks the shadow set members as being improperly
dismounted and requires a merge operation.
If you dismount a virtual unit while a copy operation
is in progress for the shadow set, the copy operation aborts and
the shadow set is dissolved. You receive OPCOM messages similar
to those in the following example:
$ DISMOUNT DSA9999: %%%%%%%%%%% OPCOM 24-MAR-1990 20:29:57.52 %%%%%%%%%%% $7$DUA6: (WRKDSK) has been removed from shadow set. %%%%%%%%%%% OPCOM 24-MAR-1990 20:29:57.68 %%%%%%%%%%% $7$DUA56: (PLADSK) has been removed from shadow set. %%%%%%%%%%% OPCOM 24-MAR-1990 20:29:57.88 %%%%%%%%%%% Message from user SYSTEM on SYSTMX
Dismounting
Shadow Sets in Site-Specific Shutdown Procedures Site-specific shutdown command procedures can be created for
each system in your cluster, as described in the OpenVMS System
Manager's Manual. The default SHUTDOWN.COM procedure that
ships with the operating system performs a DISMOUNT/ABORT/OVERRIDE=CHECKS
operation on all mounted volumes. If files are left open on any
mounted shadow sets, a merge operation will be required for these
shadow sets when the system is rebooted.
To prevent such unnecessary merge operations, HP recommends
that you modify each site-specific SYSHUTDWN.COM command procedure
to dismount the shadow sets without using the DISMOUNT/ABORT/OVERRIDE=CHECKS
qualifiers. If open files are found, they should be closed.
Dismounting and Remounting With One Less
Member for Backup As discussed in
Dissolving Shadow Sets, the virtual unit can be dismounted on the system
or across an OpenVMS Cluster system. To ensure that the virtual
unit has been dismounted correctly, the following steps are recommended:
Issue the MOUNT/NOWRITE
command, followed by the SHOW DEVICE command, for example:
$ MOUNT/NOWRITE DSA42: /SHADOW=($4$DUA3,$4$DUA4,$4$DUA5) volume-label
$ SHOW DEVICE DSA42:
Observe that the virtual unit is in a steady state;
that is, all members are consistent and no copy or merge operation
is in progress. If a copy or merge operation is in progress, you
must wait for the operation to complete.
When the virtual unit is in a steady state, remove
a member from the shadow set with the DISMOUNT command, as shown
in the following example:
$ DISMOUNT $4$DUA5
Dismount the virtual unit and then remount it with
one less member, as shown by the following command:
The shadow set member that was removed can now be used for
a backup operation of the virtual unit.
If your application must run continuously (that is,
you cannot dismount the virtual unit without disrupting your business),
you can still remove a shadow set member that you plan to return
later to the shadow set. Your application and recovery procedures
must be designed to ensure data consistency, as described in
Guidelines for Using a Shadow Set Member for Backup.