3PAR InForm® OS 2.3.1 Concepts Guide (320-200112 Rev B, February 2010)

10.5
Virtual Volume Types
InForm OS Version 2.3.1 3PAR InForm OS Concepts Guide
10.2.3.1 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.
n write rate warning period
volume’s virtual size
Allocation warning = 1 —
••
percentage
•
100