HP 3PAR Policy Manager Software - Manual (Page 42)

A.4
3PAR Policy Advisor User’s Guide
Why can’t I tune Thinly-Provisioned Virtual Volumes (TPVVs) and virtual volume
snapshot space to use the same CPG?
■ Tuning operations work by creating a fixed mapping from regions in the original LDs to
regions in the new target LDs. Regions are then moved from the original source LDs to the
new target LDs. With fully-provisioned volumes, the original LD region to new LD region
mapping is fixed and doesn’t change during the tuning operation.
■ With TPVVs, the system must account for the fact that TPVVs grow by increasing the size of
the underlying LDs. Therefore, the fixed mapping cannot be maintained.
■ The storage mechanism for TPVVs is the same mechanism used for snapshot space, so the
same rules that apply to TPVVs apply to snapshot space.
What are the main factors that affect Policy Advisor performance?
■ The more virtual volumes in the system, the longer the analysis and tuning operations take
to complete.
■ Virtual volumes with shared logical disks created with the -shared option take much
longer to analyze and tune than virtual volumes with separate logical disks.
My system includes logical disks with a RAID set size of 3 but the Policy Advisor
suggests tuning operations with a set size of 2?
■ Policy Advisor attempts to make all of the virtual volumes included in the analysis the same.
This is why you should carefully review the suggestions before running any suggested
tuning operations.
■ If a virtual volume that provisions space directly from LDs was specifically created with a set
size of 3, and that virtual volume is included in the list of virtual volumes to be analyzed,
you must explicitly state the set size is 3 in the Policy Advisor options. Otherwise, the
default value of 2 will be used and the virtual volume will no longer have a set size of 3.
■ If a CPG used by a virtual volume that provisions space from CPGs is modified with the
setcpg command between the time the virtual volume was created and the time Policy
Advisor starts running, then Policy Advisor uses the current CPG settings when the tuning
operations run. You must explicitly state the set size is 3 in the Policy Advisor options.
Otherwise, the default value of 2 will be used.