Creating Bitmaps
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The DCL commands DISMOUNT and MOUNT are used for creating bitmaps. The MOUNT command is used for starting a minicopy operation using a bitmap (see “Starting a Minicopy Operation ”).
To create a bitmap, you must specify the /POLICY=MINICOPY[=OPTIONAL] qualifier with the DISMOUNT command. If you specify /POLICY=MINICOPY=OPTIONAL, a bitmap is created if there is sufficient memory. The disk is dismounted, regardless of whether a bitmap is created.
The following example shows the use of the POLICY=MINICOPY=OPTIONAL qualifier with the DISMOUNT command:
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This command removes $4$DUA1 from the shadow set and starts logging writes to a bitmap, if possible.
If you specify /POLICY=MINICOPY only (that is, if you omit =OPTIONAL) and there is not enough memory on the node to create a bitmap, the dismount fails.
You can create a bitmap with the MOUNT command under the following conditions:
The shadow set that was previously mounted was correctly dismounted.
A multiple member shadow set must have been mounted before on the same node, on another node in the same cluster, or on another node outside the cluster.
The shadow set is not currently mounted on any other node in the cluster (if the node on which you are mounting the shadow set is in a cluster).
When you mount the shadow set, you mount it minus one member.
You specify the /POLICY=MINICOPY[=OPTIONAL] qualifier to the MOUNT command.
The bitmap created with this command is used for a minicopy operation when you later mount one of the former members of the shadow set into the set.
If you specify the /POLICY=MINICOPY=OPTIONAL qualifier and the shadow set is already mounted on another node in the cluster, the MOUNT command succeeds but a bitmap is not created.