HP 3PAR InForm OS 3.1.1 Concepts Guide

TPVV Warnings and Limits
The TPVV volume size limit is 16 TB. When creating a TPVV, you have the option to set an allocation
warning threshold and an allocation limit threshold.
• allocation warning threshold: For volumes capable of allocating space on demand, the
user-defined threshold at which the system generates an alert. This threshold is a percentage
of the volume's virtual size, the size that the volume presents to the host.
• allocation limit threshold: For volumes capable of allocating space on demand, the user-defined
threshold at which writes fail, preventing the volume from consuming additional resources.
This threshold is a percentage of the volume's virtual size, the size that the volume presents
to the host.
When setting TPVV allocation warnings and allocation limits, you must take into account the space
to be consumed by both the volume’s user data and the snapshot data.
The total amount of snapshot space consumed by a TPVV and its snapshots includes the data written
to the base volume and the data written to the snapshots. The size of the data written to the snapshots
equals the total writes to the base volume since the oldest existing read-only (RO) snapshot was
created.
When deciding on the allocation warning and allocation limit thresholds for a TPVV, you can use
an estimate of the maximum write rate to compute the snapshot data growth rate.
• If there are no RO snapshots, and the volume is not a physical copy or used for Remote Copy,
use the maximum write rate as the growth rate.
• If there are RO snapshots, or if the volume is not a physical copy or used for Remote Copy,
use twice the maximum write rate as the growth rate.
• Set the allocation warning and limit thresholds based on the growth rate and how much
advance warning you require before the volume reaches its limit and writes fail.
Use the following formula to generate the allocation warning threshold:
where the value of n is as follows:
• for a TPVV without read-only snapshots, and when that TPVV is not a physical copy or used
for Remote Copy, n=1.
• for a TPVV with read-only snapshots, or when that TPVV is a physical copy or used for Remote
Copy, n=2.
For example, if a 1 TB TPVV with read-only snapshots has a maximum write rate of 1 GB per day
and you would like 30 days warning prior to that TPVV reaching the allocation limit, use the
following calculation for the allocation warning percentage:
Physical Copies
A physical copy is a point-in-time copy that duplicates all the data from one original base volume
to another volume called the destination volume. This is done so that the data on the destination
volume can be used if the original base volume becomes unavailable. Any changes to either volume
Physical Copies 45