Selecting The Proper Dynamic Capacity Policy Thresholds - HP 418800-B21 - StorageWorks Modular Smart Array 70 Storage Enclosure User Manual

Hp storageworks replication solutions manager 4.0.1 user guide (t3680-96308, june 2008)
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Host volume configuration
LVM and Veritas online JFS
Non-LVM and Veritas online JFS
LVM and VxFS without online JFS.
Non-LVM and VxFS without
online JFS.
HFS filesystem
LVM and VxFS with or without
online JFS
Non-LVM and VxFS with or
without online JFS
HFS filesystem
1
If the host volume is not part of a volume group, taking it offline involves unmounting it. If the host volume is part of a volume
group, taking it offline involves unmounting it and deactivating the volume group.
2
Policies are supported only for single virtual disk host volumes.
3
Requires installation of the vgmodify tool. This tool is part of the HPUX patch PHCO_35524 for 1 1.23.

Selecting the proper dynamic capacity policy thresholds

When setting a dynamic policy, the following guidelines apply:
Use an extend threshold of 75% or greater.
Use a shrink threshold of 35% or less.
Use an increment value of approximately 10% of the current host volume size. For example, if the
current size is 50 GB use an increment value of 5 GB.
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
156
Host volumes
Policy
VxVM
VxVM
Extend support?
HP-UX 1 1.31
1
Manual (offline
only)
2
and manual (online)
Manual (offline
1
only)
Manual (offline
1
only)
None
None
HP-UX 1 1.23
Manual
3,
(offline
1
only)
Manual (offline
1
only)
None
None
Shrink support?
None
Policy
2
and manual (online)
None
None
None
None
None
Manual (offline
1
only)
None
None

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