To create a shadow set, you must use the MOUNT command
with the /SHADOW qualifier to mount at least one physical disk into
a shadow set and assign a virtual unit name to the set, as shown in Example 4-1.
Example 4-1 Creating a Shadow Set
$MOUNT DSA23: /SHADOW=$4$DUA9: volume-label logical-name |
This
example forms a shadow set represented by the virtual unit DSA23,
and includes one shadow set member, $4$DUA9. To create a shadow set,
you must observe the following rules:
Use the DSAn: format to name the shadow set virtual unit, where
n represents a unique number from 0 through 9999. If you do not include
a number after the DSA prefix, MOUNT automatically assigns the highest
unit number available. Numbering starts at 9999 and decrements to
0; the first virtual unit mounted is numbered 9999, the second 9998,
and so on.
Each virtual unit number
must be unique across the system, regardless of whether or not the
unit is mounted for public (mounted with the /SYSTEM qualifier) or
private access. Virtual units are named independently of the controllers
involved.
The /SHADOW qualifier
is required when specifying a physical device. You must name at least
one physical device as a parameter to the /SHADOW qualifier. Although
one-member shadow sets are valid, you must mount one or two additional
disks in order for the shadowing software to maintain duplicate data.
Adding disks to an existing shadow set is discussed in “Adding Shadow Set Members ”.
Use a nonzero allocation
class for each physical device in the shadow set. Use the allocation
class naming format $allocation-class$ddcu, where:
allocation-class is a numeric value from 1 to 255.
dd describes the device type of the physical device (for example, DU,
DK, or DG).
c is a letter from A to Z that represents the controller designation.
Note that you cannot use more than 3 characters for the ddc portion of the name. Failure to observe this requirement
results in failure to mount the shadow set.
u is the unit number of the device.
Note that you cannot
use more than 3 letters for the ddc portion of the name.See HP OpenVMS
Cluster Systems for more information about allocation classes.
Specify a 1- to 12-character
volume label for the virtual unit.
Optionally, specify a
1- to 255-alphanumeric-character logical name string for the shadow
set.
In addition, you can specify /SYSTEM, /GROUP,
or /CLUSTER to make the shadow set available to all users of a system,
all members of a group, or all nodes in a cluster on which shadowing
is enabled.
To create a three-member shadow set, you can add
two members in a single MOUNT command to an existing one-member shadow
set. This method optimizes the I/O operation because both members
are copied at the same time. (See the example in “Creating a Shadow Set With /SYSTEM and With /CLUSTER ”.)
You can also streamline the process of creating
a shadow set by initializing multiple devices in one command, using
INITIALIZE/SHADOW/ERASE, as described in “Using INITIALIZE/SHADOW/ERASE to Form a Shadow Set (Integrity
servers and Alpha)”.
Upon receiving a command to create a shadow set,
the volume shadowing software may perform a copy or a merge operation
to reconcile data differences. If you are not sure which disks might
be targets of copy operations, you can specify the /CONFIRM or /NOCOPY
qualifiers as a precaution against overwriting important data when
you mount a disk. These and other MOUNT command qualifiers are discussed
in “MOUNT Command Qualifiers for Shadowing”.
