HP 3PAR Operating System Software - Manual (Page 188)

Basic Information about CPGs
CAUTION: For a complete list of warnings and cautions regarding CPGs, refer to the HP 3PAR
InForm OS Concepts Guide.
•
CPGs require careful planning and monitoring to prevent them from becoming so large that
they set off the system's built-in safety mechanisms. These safety mechanisms are designed to
prevent a CPG from consuming all free space on the system, but they only work properly on
systems that are planned carefully and monitored closely.
•
HP strongly recommends that you associate a maximum of 32 volumes with a single CPG
because:
◦ Virtual volumes in the same CPG can share the same logical disk. If the logical disk is
damaged (for example, because of multiple simultaneous disk failures), all the volumes
associated with that logical disk become unavailable.
◦ Performance of operations related to virtual volumes can suffer if there is too much
interleaving within the logical disks.
Creating a CPG
To create a CPG, see the HP 3PAR InForm OS CLI Administrator’s Manual.
Virtual Volumes Used with Remote Copy
There are two types of virtual volumes you can use with Remote Copy. These virtual volumes draw
different amounts of space from the Common Provisioning Group (CPG) with which they are
associated.
CPG Space Allocated Type of Virtual Volume
All data and snapshot space is allocated on demand from the CPG. Thinly Provisioned Virtual Volumes (TPVVs)
Only snapshot space is allocated on demand from the CPG. Fully provisioned virtual volumes
Thinly Provisioned Virtual Volumes
A Thinly Provisioned Virtual Volume (TPVV) draws space as necessary from the CPG with which it
is associated. The CPG allocates space on demand in small increments.
•
By default, TPVVs do not have snapshot space. To use TPVVs with Remote Copy, you must
create TPVVs with snapshot space.
•
When you perform the initial synchronization of a TPVV that is configured as a primary Remote
Copy virtual volume, Remote Copy sends only the allocated data pages to the secondary
virtual volume on the backup system.
•
When you configure a TPVV as a primary virtual volume in a Remote Copy volume group,
you must make sure that either the secondary virtual volume has no data written to it before
you add it to the Remote Copy volume group, or that it matches the primary volume. If
nonmatching data exists in the secondary virtual volume, the initial synchronization fails.
For more information on creating a TPVV, see the HP 3PAR InForm OS CLI Administrator’s Manual.
Fully Provisioned Virtual Volumes
Fully provisioned virtual volumes only draw snapshot space from the CPG.
For more information on creating a fully provisioned virtual volume, see the HP 3PAR InForm OS
CLI Administrator’s Manual.
188 Virtual Volumes and CPGs