HP P6000 Replication Solutions Manager User Guide (T3680-96089, October 2012)

NOTE: Not following the above guidelines can result in a situation where the values used to set
one policy may prevent you from setting the opposite policy. For example, if inappropriate values
are used to set an extend policy, they may prevent you from setting a shrink policy on the same
host volume. In this situation, you will be informed that the shrink policy option is not available for
the selected host volume. If this situation occurs, reset the policy values using the above guidelines.
When setting a dynamic capacity policy threshold, you must be aware of the interaction between
the extend and shrink policy values. RSM will not allow you to select threshold values that could
result in cyclic resize—a condition in which the host volume goes into a loop resizing itself. If you
attempt to select a policy threshold that would result in cyclic resize, RSM alerts you and recommends
a policy threshold that will avoid the situation.
For example, assume you have a 1 GB host volume on which you have set a shrink policy threshold
of 10% and an extend policy threshold of 50%. The desired increment size is 5 GB. When the
host volume capacity reaches 0.5 GB (50% of 1 GB) the extend policy is triggered, extending the
host volume size to 6 GB (1 GB + 5 GB increment). This causes the host volume capacity to drop
to 8.33%, which invokes the shrink policy (<10%). This in turn causes extend policy to be
retriggered. The host volume would now be in cyclic resize.
Manually resizing a host volume on which you have set a policy should be done with care. The
manual resize will be performed, but interaction with the existing policy may cause undesired
results. For example, assume you manually extend a host volume on which a shrink policy has
been set. The manual extend will be implemented, but the larger size of the host volume may cause
the shrink policy to be triggered at the next refresh cycle, causing the size of the host volume to
be reduced.
Using DC-Management with replication
Guidelines for using DC-Management with HP P6000 Business Copy
• You cannot use DC-Management with snapshots or mirrorclones created using HP P6000
Business Copy. You cannot use DC-Management on the source or the replica.
• You can resize a snapclone once normalization is complete. During normalization, you cannot
use DC-Management on a snapclone.
• If you set a dynamic policy on a host volume and then create a snapshot or mirrorclone on
the underlying virtual disk, the policy will not be executed properly. When the policy threshold
is reached, the policy will trigger and the associated job will be created. However, the job
will fail with a message indicating the resize cannot be performed because a replica exists
on the virtual disk. You should disable or remove the policy to prevent it from running.
Guidelines for using DC-Management with HP P6000 Continuous Access
• When the source virtual disk of a DR pair is extended using DC-Management, the size of the
destination virtual disk is increased automatically. If the destination array does not have enough
capacity to increase the size of the virtual disk, the attempt to extend the source virtual disk
fails. The automatic increase of the destination virtual disk does not require a DCM license
on the destination array. The increase is enabled by the CA license.
• RSM checks for a DCM license on the source array only. If the destination array does not
have a DCM license, it will stop working after a fail over.
• You cannot shrink a destination DR group member.
• You cannot extend a DR group destination.
• You cannot extend a source virtual disk if the DR link is suspended.
142 Host volumes