HP 3PAR System Reporter Software - Manual (Page 181)

NOTE: When you specify two tiers, for the purposes of analysis and data movement only the
order of the tiers matters, not the actual tier number. For example specifying tiers 0 and 1 is
equivalent to specifying 0 and 2 or 1 and 2. The lower numbered tier is considered the faster tier
and the higher numbered tier is considered the slower tier.
However, you should consider whether you may want to add a tier in the future, and if so what
tier number that is likely to be, and leave out that tier number for the two tier configuration. For
example, if you have SSD PDs and NL PDs, you may want to use SSD PDs for the tier 0 CPG, NL
PDs for the tier 2 CPG, and leave tier 1 empty for the possibility of a CPG using FC PDs.
The maximum space in GiB for the tier allows you to limit how much space in a tier is available
for a given configuration. If you do not want to place a limit on the amount of space for a tier, you
can enter a large value that is unlikely to be exceeded.
Adaptive Optimization looks at several limits on the CPG:
•
The CPG allocation (hard) limit
•
The CPG warning limit
•
The AO space limit for the tier
Adaptive Optimization takes the minimum of these limits and treats that as a space limit for the
CPG and attempts to keep the total LD used space in the CPG below this limit (by a margin of
about two times the grow size of the CPG).
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 HP 3PAR Storage System 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,
Configuring Adaptive Optimization 181