HP StorageWorks SAN Virtualization Services Platform Manager user guide (5697-0295, January 2010)

Creating PiTs
You can create a PiT on the following storage elements:
• A virtual disk. However, you cannot create a PiT on one of the domain’s setup virtual disks.
• A snapshot.
• A VDG.
• A VDG snapshot.
See the HP StorageWorks SAN Virtualization Services Platform release notes for the number of PiTs
and snapshots that can be created on a virtual disk, and the minimal interval between PiTs.
When successively creating multiple PiTs on one element, you cannot create each PiT until the previous
PiT’s status is normal.
When you create a PiT, VSM allocates a temporary virtual disk to be used for keeping all upcoming
data modifications. The temporary virtual disk exists as long as the PiT exists and is allocated from
the storage pool from which the original element is allocated. All I/O writes to the original element
are redirected to the temporary virtual disk that was allocated for saving data modifications. The data
of the original element remains unchanged.
The temporary virtual disk is created with a small initial size and expands with subsequent data
updates. For information about verifying that the storage pool has enough free capacity to handle
PiTs, see “Planning storage pool capacity for snapshots and PiTs” on page 237.
When you create a PiT on a VDG or VDG snapshot, a PiT is actually created on each VDG member.
Each temporary virtual disk created to store the subsequent data updates of a VDG member is allocated
from the same storage pool from which the VDG member is allocated.
NOTE:
When you create a PiT, the PiT freezes the virtual disk data according to the data in the physical
storage system at the exact time that the PiT is created. In order to snapshot a consistent image of
data, verify that the application flushes all updates to back-end LUs prior to PiT creation. If the
application is able to complete all pending transactions and flush work caches, then this is called
transactional consistency . This is different than crash consistency , where members may contain
incomplete or partial transactions.
To create a PiT:
1. Right-click the element on which you want to create a PiT.
2. Select Manage > Snapshot Service> Create PiT. The Create PiT wizard opens to the Enter PiT
parameters screen.
3. In the PiT name field, enter a name for the PiT.
4. In the Comment field, optionally enter text. You can use this field for any purpose.
5. Click Next. The Select Folder screen appears.
6. If you want to add the PiT to a folder, enter the folder name in the Folder field or click Browse to
browse to the folder. The folder must already be created. For information about creating folders,
see “Creating folders” on page 315.
7. Click Next. A confirmation screen appears.
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