3PAR InForm® OS 2.2.4 Concepts Guide (320-200085 Rev B, March 2009)

8.13
Virtual Volume Types and Variations
InForm OS Version 2.2.4 3PAR InForm OS Concepts Guide
To learn about CPGs, see Chapter 10, Common Provisioning Groups. For instructions on
creating CPGs and TPVVs, refer to the InForm OS CLI Administrator’s Manual or the InForm OS
Management Console Online Help.
8.7.5 TPVV Warnings and Limits
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 copy data.
The total amount of Snapshot Data (SD) 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 SD growth rate.
■ If there are no RO snapshots and the volume is not used for Physical Copy or Remote Copy,
use the maximum write rate as the growth rate.
■ If there are RO snapshots or the volume is used for Physical Copy or Remote Copy, use twice
the maximum write rate as the growth rate.
CAUTION: Do not allow the volumes that draw from a CPG to exceed the CPG’s
growth limit (see TPVV Warnings and Limits, below). Doing so can invalidate
snapshot volumes. Refer to Common Provisioning Groups on page 10.1 for
additional cautions and instructions.