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

7.2

Logical Disks and Common Provisioning Groups

3PAR InForm OS Concepts Guide InForm OS Version 2.2.4

7.2 Logical Disks and Common Provisioning Groups

Creating a Common Provisioning Group (CPG) establishes a virtual pool of logical disks that can

grow on demand. Volumes associated with a CPG draw logical disk space from that pool as

needed, allocating space on demand. As the volumes that draw from a CPG require additional

storage, the system automatically creates additional logical disks and adds them to the pool.

When you create a CPG, the system creates all underlying logical disks for you automatically.

For instructions on creating CPGs and their underlying logical disks, see the InForm OS CLI

Administrator’s Manual or the InForm OS Management Console Online Help.

Once you create a CPG, you can add and remove logical disks. You can also specify advanced

logical disk parameters when creating CPGs. This allows you to exercise a greater degree of

control over how the system creates logical disks within the CPG. To learn how, see the InForm

OS CLI Administrator’s Manual or the InForm OS Management Console Online Help.

7.3 Logical Disk Types

The system sets aside Logical Disks (LDs) for logging, for preserved data, and for system

administration. All other logical disks are available for user and snapshot data (when

applicable).

The following logical disk types can exist on the same system:

■ Logging LDs can be used to temporarily hold data during disk failures and disk replacement

procedures. Each controller node in the storage server has one RAID 1 logging logical disk.

■ Preserved data LDs can be used to hold preserved data. The size of the preserved data

logical disk is based on the amount of data cache in a system.

When disk failures during write operations leave data suspended in cache memory, the

system temporarily preserves this data by writing it to a preserved data logical disk. By

doing so, the system clears the data cache and prevents it from locking up and leading to

wider system failures. When the destination logical disks become available again, the

system automatically writes the preserved data from the preserved data LDs to the

destination LDs.

■ Administration LDs hold the snapshot administration data for virtual volumes (when

applicable)

, including volumes that draw from the logical disks in a Common Provisioning

1 Snapshot functionality requires additional licenses and may not be available on your system.