HP 3PAR StoreServ Concepts Guide: HP 3PAR OS 3.1.3

on different CPGs, the user space remains available to the host if the CPG containing the snapshot
space becomes full. To save time, you can create many identical virtual volumes at one time.
If your system is accessible from an OpenStack cloud, you may see volumes with prefixes indicating
that the volumes were created through the OpenStack cloud. Volumes created through the OpenStack
cloud use the OpenStack Volume (OSV) and OpenStack Snapshot (OSS) prefixes.
Administrative Volumes
As part of installation and setup process, the administrative volume is created on the system. This
volume is used by the system to store administrative data such as the system event log. The
administrative volume is always named admin. This volume cannot be exported and cannot be
removed from the system.
CAUTION: It is strongly recommended that you do not tamper with the admin volume.
Fully-provisioned Virtual Volumes
An FPVV is a volume that uses LDs that belong to a CPG. Unlike TPVVs, FPVVs have a set amount
of user space allocated in the system for user data. They require the system to reserve the entire
amount of space required by the FPVV whether or not the space is actually used. The FPVV size
is fixed, and the size limit is 16 TB. You can set snapshot space allocation limits and usage warnings
to help manage the growth of snapshot space.
Thinly Provisioned Virtual Volumes
With an HP 3PAR Thin Provisioning Software license, you can also create TPVVs. A TPVV uses LDs
that belong to a CPG. TPVVs associated with the same CPG draw user space from that pool,
allocating space on demand in one chunklet increments, beginning with 256 MB per controller
node or 1 GB per controller node. As the volumes that draw space from the CPG require additional
storage, the system automatically creates additional LDs and adds them to the pool until the CPG
reaches the user-defined growth limit that restricts the CPG maximum size. The TPVV volume size
limit is 16 TB.
TPVVs can respond to host write requests by allocating space on demand in one chunklet increments,
beginning with 256 MB per controller node or 1 GB per controller node. These allocations are
adaptive, because subsequent allocations are based on the rate of consumption for previously
allocated space.
For example, if a TPVV is initially allocated 256 MB per node, but consumes that space in less
than sixty seconds, the next allocation becomes 512 MB per node. However, if the initial 256 MB
per node is consumed more slowly, the next allocation increment remains at 256 MB per node.
Under this provisioning scheme, the maximum allocation increment is 1 GB per controller node
that supports the TPVV. In addition, as the TPVV reaches either its exported size or its user-defined
allocation limit, the system allows allocation of an additional 128 MB per node beyond these
limits, to ensure that the exported TPVV address space is usable.
CAUTION: Use of allocation limits is recommended to prevent consumption of physical raw
capacity beyond a tolerable limit. However, you should exercise caution when you set the value
of the allocation limit. When the allocation limit is reached, any new writes to TPVVs will fail, or
snapshot volumes associated with the CPG may become invalid. Under this condition, some host
applications do not handle write failures gracefully and may produce unexpected failures.
CAUTION: Do not allow the volumes that draw from a CPG to exceed the CPG growth limit.
Doing so can invalidate snapshot volumes. See “Common Provisioning Groups” (page 41) for
additional cautions and recommendations.
Virtual Volume Types 45