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

2.8
3PAR Storage Concepts and Terminology
3PAR InForm OS Concepts Guide InForm OS Version 2.2.4
A base volume is the original volume from which a series of point-in-time copies (snapshots),
either physical or virtual, can be created. Base volumes differ from other types of virtual
volumes in that base volumes are the only type of volumes that have physical storage space to
hold data rather than pointers to other volumes.
A base volume has three separate components:
■ User space, the area of the volume that corresponds to logical disk regions holding data
that is seen by the host to which the volume is exported as a LUN. These logical disk regions
hold volume user data.
■ Snapshot data space (optional), also known as copy space, corresponds to logical disk
regions holding data that has been changed since a snapshot, or point-in-time copy, of the
volume was created.
1
These logical disk regions hold volume copy data.
■ Snapshot administration space (optional), also known as admin space, corresponds to
logical disk regions that track changes to the volume since a snapshot
1
was created. These
logical disk regions hold pointers to the snapshot data space, which contains the latest
changes made to a volume.
The snapshot data and snapshot administration spaces for a given base volume are used for all
of the virtual copies created from that parent volume. If either of these spaces becomes full,
the copy-on-write operation (virtual copy) fails. Base volumes are always read/write volumes.
Read-only base volumes cannot be created. See Chapter 8, Virtual Volumes for information on
creating base volumes and snapshots.
In addition to standard base volumes, two base volume variations allow the system to allocate
space on demand: thinly provisioned virtual volumes (TPVVs) and commonly provisioned
virtual volumes (CPVVs).
2
Base volume variations are described in more detail in Chapter 8,
Virtual Volumes and Chapter 10, Common Provisioning Groups.
2.1.3.2 Physical Copies
A physical copy duplicates (creates a snapshot of) all the data from its base volume onto
another base volume, the destination volume, for use should the original volume become
unavailable. However, unlike a virtual copy, a physical copy has the performance of a base
virtual volume.
A physical copy can only be created from a base volume with enough free snapshot data space
to accommodate writes to that volume during the physical copy operation. In addition, the
1 Creating snapshots may require additional licenses.
2 Creating TPVVs and CPVVs may require additional licenses.