HP Command View EVA Software - Manual (Page 34)

Mirrorclone migration
XCS 10000000 and later controller software supports online mirrorclone migration, which allows
you to switch the identities (LUN WWNs), and thus the properties, of a source virtual disk with its
synchronized mirrorclone. The migration is accomplished without impacting presentations or host
I/O to the virtual disks. Data is not actually moved.
The online mirrorclone migration features are part of the HP P6000 Business Copy license.
Migrations can occur only if a valid instant-on or permanent HP P6000 Business Copy license is
present.
Thin provisioning
Thin provisioning is a feature of HP P6000 storage systems that allows you to create and manage
thin provisioned virtual disks. The maximum capacity of a thin provisioned virtual disk can differ
from its allocated capacity. When a thin provisioned virtual disk is created, the user specifies a
maximum capacity, and the reserved capacity is set to zero. As writes occur, disk space is
dynamically allocated, but reserved capacity and maximum capacity remain unchanged. The
space allocated does not need to be contiguous. In the event that the allocated capacity reaches
the physical disk capacity, the write operation fails.
EVA thin provisioned virtual disks also support unmap request (de-allocate or free the disk space)
sent by the host (VMware ESX 5.1x and Windows Server 2012). As unmap occur, disk space is
dynamically de-allocated, but reserved capacity and maximum capacity of the virtual disk remains
unchanged.
Thin provisioned virtual disks differ from standard virtual disks as follows:
Standard virtual disk Thin provisioned disk
Requires the full amount of physical disk space to be
allocated at all times The amount of physical disk space allocated can
automatically change in response to the amount of data
being stored, up to the specified size of the virtual disk or
until all available disk space is used
Must be explicitly resized whenever the amount of disk
space needs to be changed Does not require explicit resizing (manually or with scripts)
Physical disk space that is allocated but unused can create
stranded capacity Has no unused physical disk space
The requested capacity is limited by the amount of
available physical disk capacity that can be allocated The maximum requested capacity can exceed the amount
of available physical disk capacity that can be allocated
The following example demonstrates thin provisioning:
A storage administrator is planning to create two virtual disks for two new host applications. His
HP P6000 storage system currently has a total capacity of 10 TB, with 6 TB unused disk space.
The administrator determines that each host application initially requires 2 TB of disk space, but
eventually, the host applications will require 4 TB of space. With these requirements in mind, the
administrator creates two 4 TB thin provisioned virtual disks.
Each host application recognizes a 4 TB virtual disk, even though initially only 2 TB of physical
disk space is allocated. As the amount of stored data increases, the storage system automatically
allocates more space (up to the 4 TB maximum size). And, even though only 6 TB of space is
available on the storage system, the administrator is able to add 2 virtual disks with a total potential
capacity of 8 TB.
Administrator can use email notifications (Thin provisioned Vdisk capacity alarms) to monitor
respective vdisk space allocations. This facility sends email notifications when the space allocation
goes beyond allocation alarm level or comes back to normal level. These events are also logged
in Controller Events.
34 Provisioning storage