HP MSA 1040 HP MSA 1040 SMU Reference Guide (762784-001, March 2014) - Page 25

About the Volume Copy feature, The following illustrates how volume copies are created.

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About the Volume Copy feature Volume Copy enables you to copy a volume or a snapshot to a new standard volume. While a snapshot is a point-in-time logical copy of a volume, the volume copy service creates a complete "physical" copy of a volume within a storage system. It is an exact copy of a source volume as it existed at the time the volume copy operation was initiated, consumes the same amount of space as the source volume, and is independent from an I/O perspective. Volume independence is a key distinction of a volume copy (versus a snapshot, which is a "virtual" copy and dependent on the source volume). Benefits include: • Additional data protection. An independent copy of a volume (versus logical copy through snapshot) provides additional data protection against a complete master volume failure. If the source master volume fails, the volume copy can be used to restore the volume to the point in time the volume copy was taken. • Non-disruptive use of production data. With an independent copy of the volume, resource contention and the potential performance impact on production volumes is mitigated. Data blocks between the source and the copied volumes are independent (versus shared with snapshot) so that I/O is to each set of blocks respectively; application I/O transactions are not competing with each other when accessing the same data blocks. The following figure illustrates how volume copies are created. Creating a volume copy from a standard or master volume Source volume Transient snapshot Data transfer New volume 1. Volume copy request is made with a standard volume or a master volume as the source. 2. If the source a standard volume, it is converted to a master volume and a snap pool is created. 3. A new volume is created for the volume copy, and a hidden, transient snapshot is created. 4. Data is transferred from the transient snapshot to the new volume. 5. On completion, the transient volume is deleted and the new volume is a completely independent copy of the master volume, representing the data that was present when the volume copy was started. Creating a volume copy from a snapshot Master volume Snapshot(s) Data transfer New volume 1. A master volume exists with one or more snapshots associated with it. Snapshots can be in their original state or they can be modified. 2. You can select any snapshot to copy, and you can specify that the modified or unmodified data be copied. 3. On completion, the new volume is a completely independent copy of the snapshot. The snapshot remains, though you can choose to delete it. Figure 3 Creating a volume copy from a master volume or a snapshot Snapshot operations are I/O-intensive. Every write to a unique location in a master volume after a snapshot is taken will cause an internal read and write operation to occur in order to preserve the snapshot data. If you intend to create snapshots of, create volume copies of, or replicate volumes in a vdisk, ensure that the vdisk contains no more than four master volumes, snap pools, or both. For example: 2 master volumes and 2 snap pools; 3 master volumes and 1 snap pool; 4 master volumes and 0 snap pools. System concepts 25

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System concepts
25
About the Volume Copy feature
Volume Copy enables you to copy a volume or a snapshot to a new standard volume.
While a snapshot is a point-in-time logical copy of a volume, the volume copy service creates a complete “physical”
copy of a volume within a storage system. It is an exact copy of a source volume as it existed at the time the volume
copy operation was initiated, consumes the same amount of space as the source volume, and is independent from an
I/O perspective. Volume independence is a key distinction of a volume copy (versus a snapshot, which is a “virtual”
copy and dependent on the source volume).
Benefits include:
•
Additional data protection. An independent copy of a volume (versus logical copy through snapshot) provides
additional data protection against a complete master volume failure. If the source master volume fails, the volume
copy can be used to restore the volume to the point in time the volume copy was taken.
•
Non-disruptive use of production data. With an independent copy of the volume, resource contention and the
potential performance impact on production volumes is mitigated. Data blocks between the source and the
copied volumes are independent (versus shared with snapshot) so that I/O is to each set of blocks respectively;
application I/O transactions are not competing with each other when accessing the same data blocks.
The following figure illustrates how volume copies are created.
Figure 3
Creating a volume copy from a master volume or a snapshot
Snapshot operations are I/O-intensive. Every write to a unique location in a master volume after a snapshot is taken
will cause an internal read and write operation to occur in order to preserve the snapshot data. If you intend to create
snapshots of, create volume copies of, or replicate volumes in a vdisk, ensure that the vdisk contains no more than
four master volumes, snap pools, or both. For example: 2 master volumes and 2 snap pools; 3 master volumes and
1 snap pool; 4 master volumes and 0 snap pools.
Source volume
Transient snapshot
Data transfer
New volume
1. Volume copy request is made with a standard volume or a master volume as the source.
3. A new volume is created for the volume copy, and a hidden, transient snapshot is created.
4. Data is transferred from the transient snapshot to the new volume.
5. On completion, the transient volume is deleted and the new volume is a completely independent copy of
the master volume, representing the data that was present when the volume copy was started.
Creating a volume copy from a standard or master volume
Master volume
Snapshot(s)
Data transfer
New volume
1. A master volume exists with one or more snapshots associated with it. Snapshots can be in their original
Creating a volume copy from a snapshot
state or they can be modified.
2. You can select any snapshot to copy, and you can specify that the modified or unmodified data be copied.
3. On completion, the new volume is a completely independent copy of the snapshot. The snapshot remains,
though you can choose to delete it.
2. If the source a standard volume, it is converted to a master volume and a snap pool is created.