HP 3PAR Operating System Software - Manual (Page 46)

11 Virtual Volumes
Virtual volumes are the only data layer visible to host systems.
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Virtual volumes draw storage space from CPGs.
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Virtual volumes become visible to host systems when you export (present) them to hosts.
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Virtual volumes are exported as LUNs to hosts.
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You can create physical copies or virtual copies (snapshots) of virtual volumes. These copies
serve as backups in case the original base volume becomes unavailable.
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If you have multiple volumes that require the same administrative procedures, you can group
those volumes into an autonomic group and manage them together, as one volume.
To create and manage virtual volumes, use the HP 3PAR Management Console. For more
information, see the HP 3PAR Management Console Online Help.
Virtual Volume Types
There are three types of virtual volumes used directly for data storage:
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Fully provisioned virtual volumes have a set amount of allocated user space. Fully provisioned
virtual volumes require the HP 3PAR StoreServ Storage system to reserve the entire amount of
storage space configured for the volumes, whether or not the space is actually used. The size
of each fully provisioned virtual volume size is fixed (and not dynamic, like a Thin volume),
and the size limit is 16 TB.
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Thinly Provisioned Virtual Volumes (TPVVs or Thin volumes) draw space from the associated
CPG pools as needed. CPGs allocate space on demand to Thin volumes in small increments
for each controller node, but can adjust the size of these increments based on the rate of
consumption (allocating more space during periods of high consumption and less space during
periods of low consumption). As the volumes that draw space from the CPG require additional
storage, the HP 3PAR OS automatically adds more storage space to the CPG until the CPG
reaches its growth limit. The Thin volume size limit is 16 TB.
Monitoring Thin Volume Growth
Thin volumes require careful planning and monitoring to prevent them from becoming so large
that they set off the HP 3PAR StoreServ Storage system's built-in safety mechanisms or that
writes to the volumes fail. To restrict a Thin volume’s growth:
◦ Set an allocation warning .
◦ Set an allocation limit and ensure that this limit does not exceed the associated CPG’s
growth limit .
◦ Continue to monitor Thin volume growth.
Creating Thin volumes requires the HP 3PAR Thin Provisioning Software license.
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Administrative volumes are created by the system and are for system usage only.
46 Virtual Volumes