HP P6000 Replication Solutions Manager User Guide (T3680-96089, October 2012)

Fully allocated snapshots
When a snapshot is fully allocated, the storage system initially allocates an amount of space that
is equal to the capacity of the source virtual disk, plus a small amount of space for point-in-time
information and pointers to data on the source. As data is over-written on the source, the controller
copies the original (point-in-time) data from the source to the snapshot. The amount of space
allocated on the snapshot never changes.
Once created, a fully allocated snapshot cannot run out of space.
Thin provisioning
Thin provisioning is a licensed feature that allows you to specify the capacity of a virtual disk when
you create it. The physically allocated space will dynamically increase from 0 to its requested
capacity as data is added to the virtual disk.
You can set thresholds on a thin provisioned virtual disk and its disk group to alert you when the
disk allocation is approaching capacity.
NOTE: This feature requires both an HP P6000 Command View license and an HP Thin
Provisioning license.
The key features of thin provisioned virtual disks differ from standard virtual disks in several
significant ways:
• The amount of physical disk space which is allocated to a thin provisioned virtual disk can
automatically change in response to the amount of data being stored, up to the specified size
of the virtual disk. A traditional virtual disk requires the full amount of physical disk space to
be allocated at all times.
• A well planned thin provisioned virtual disk does not require explicit resizing (manually or
with scripts). With a traditional virtual disk, any time the size needs to be changed, it must
be explicitly resized.
• There is no unused physical disk space associated with a thin provisioned virtual disk, thus
physical disk space cannot become stranded. With a traditional virtual disk, the allocated but
unused physical disk space can create stranded capacity.
• The requested capacity for a thin provisioned virtual disk can actually exceed the amount of
physical disk drive capacity that can be allocated. This is not possible with traditional virtual
disks. (An example is also provided in the OLH.)
The following restrictions apply to thin provisioned virtual disks:
• You must have a valid HP Thin Provisioning license to create or modify a thin provision virtual
disk.
• You cannot create a snapshot, snapclone, or mirrorclone from a thin provision virtual disk.
• A thin provisioned virtual disk cannot be included in a remote replication DR group.
• When creating a thin provisioned virtual disk, you cannot request a capacity greater than:
The largest virtual disk capacity of a corresponding RAID level in the array◦
◦ The largest virtual disk capacity of a corresponding RAID level in the disk group
◦ 32 TB
CAUTION: An array’s addressable capacity value is commonly larger than the maximum supported
capacity of the array. The controller software prevents oversubscribing of the addressable capacity
limitation, but will not prevent oversubscribing the physical limitations of the LDAD (logical disk
addressable space) or array. If you oversubscribe the capacity, you must delete the virtual disk
from the disk group.
274 Virtual disks