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

10.5
Precautions and Planning
InForm OS Version 2.2.4 3PAR InForm OS Concepts Guide
10.2.3 Growth Warning
When the size of the volumes that draw from a CPG reach the CPG’s growth warning, the
system generates an alert to notify you of the CPG's increasing size. This safety mechanism
provides the opportunity to take early action that may prevent snapshot volumes associated
with the CPG from experiencing failures, causing host or application write failures, and
exhausting all free space on the system.
When setting growth warnings for CPGs, it is critical to consider the number of CPGs on the
system, the total capacity of the system, and the projected rate of growth for all volumes on
the system.
The storage system does not prevent you from setting growth warnings that exceed the total
capacity of the system. For example, on a 3 TB system you can create two CPGs that each have
a growth warning of 2 TB. However, if both CPGs grow at a similar rate, it is possible for the
volumes that draw from the CPGs to consume all free space on the system before either CPG
reaches the growth warning threshold.
When volumes that draw from a CPG exceed the growth warning for the CPG and a system
alert results, it is important to take action to prevent the volumes from exceeding the CPG’s
growth limit.
NOTE: The system may round up when creating logical disks to support virtual
volumes and common provisioning groups (CPGs), resulting in a discrepancy
between the user-specified size or growth increment and the actual space
allocated to logical disks created by the system. For a detailed discussion of this
issue, see Logical Disk Size and RAID Type on page 7.3.
CAUTION: Use caution in planning CPGs. The system does not prevent you from
setting growth warnings or growth limits that exceed the amount of currently
available storage on a system. When volumes associated with a CPG use all space
available to that CPG, any new writes to TPVVs associated with the CPG will fail
and/or snapshot volumes associated with the CPG may become invalid (stale).
Under these conditions, some host applications do not handle write failures
gracefully and may produce unexpected failures.