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

8.2
Logical Disks and Virtual Volumes
3PAR InForm OS Concepts Guide InForm OS Version 2.2.4
8.1 Logical Disks and Virtual Volumes
Virtual volumes are the only logical storage component visible to hosts. Virtual volumes are
built on logical disks, which are built on physical disks. Volumes are created by mapping data
from one or more logical disks, where mapping is the correspondence of a logical disk region
to a virtual volume region. Therefore, before you can create a virtual volume, you must first
create its underlying logical disks.
8.2 Standard Base Volumes
There are several types of virtual volumes, as described in Virtual Volume Types and Variations
on page 8.5.
When you create a standard base volume, the system creates all underlying logical disks for
you automatically before creating the virtual volume. See the InForm OS CLI Administrator’s
Manual or the InForm OS Management Console Online Help for basic instructions.
8.3 Thinly Provisioned Virtual Volumes
With a 3PAR Thin Provisioning license, you can also create thinly provisioned virtual volumes. A
Thinly Provisioned Virtual Volume (TPVV) uses logical disks that belong to a logical disk pool
known as a Common Provisioning Group (CPG). Thinly provisioned virtual volumes associated
with the same CPG draw space from that pool as needed, allocating space on demand in small
increments beginning with 256 MB per controller node. As the volumes that draw space from
NOTE: 3PAR Thin Provisioning and snapshot functionality are optional system
features which must be licensed separately from other 3PAR software products
and features.
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.