HP 3PAR System Reporter Software - Manual (Page 279)

9.7 Configuring Adaptive Optimization
System Reporter 2.8 3PAR System Reporter User’s Guide
The TPVV usr space and Snapshot copy space for a CPG can be examined using the InForm CLI
showvv -cpg alloc command. Since this space may need to grow on demand as the host
writes the VV or snapshot, you should make sure that the CPG associated with the TPVV usr
space and Snapshot copy space has room to grow (i.e., you should not associate TPVV usr space
with a space-constrained SSD CPG).
As an example, suppose your default TPVV usr cpg is CPG1 (tier 1), and you set a tier space limit
on tier 1 to 100GB. In between iterations of Adaptive Optimization, suppose the TPVVs grow
and the space used in CPG1 grows to 110 GB. Also, suppose the grow size is 8GB. When the
next iteration of Adaptive Optimization runs, it will try to reduce the used space in CPG1 to
100-(2*8) = 84 GB, and attempts to move 26GB from that tier to ether tier 0 or tier 2.
The reason it needs two times the grow size is that the InServ does not currently allow usr
space for fully provisioned VVs and Snap space or TPVV space to be on the same LDs so it needs
the equivalent of the grow size for both parts. This can be inefficient, especially for SSD CPGs
that are not used for automatic growth, only Adaptive Optimization movement. Therefore, it
is recommended that you decrease the grow size for SSD CPGs to the smallest possible amount,
except in the case where the CPG is the default for snapshot or base TPVV allocation as noted
in the following caution.
CAUTION: For some CPGs, especially those that use small PDs such as SSDs, the
additional buffer space in the CPG may be too large to be left unused. To
minimize the buffer space you can use the CLI to set the CPG grow size to the
smallest possible value. However, if you do so, you should make sure that the CPG
is not the default CPG for snapshot or base TPVV allocation (the CPGs shown in
the showvv -cpgalloc CLI command). The default CPG for snapshot or base
TPVV allocation should always be one that has sufficient room to grow.