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Chapter 3 Storage Arrays 3-81
Data Replication
Data replication between the primary volume and the secondary volume is managed
by the controllers and is transparent to host machines and applications. When the
controller owner of the primary volume receives a write request from a host, the
controller first logs information about the write to a mirror repository volume, then
writes the data to the primary volume. The controller then initiates a remote write
operation to copy the affected data blocks to the secondary volume at the secondary
storage array.
After the host write request has been written to the primary volume and the data has
been successfully copied to the secondary volume, the controller removes the log
record on the mirror repository volume and sends an I/O completion indication
back to the host system.
Volume Copy
This is a premium feature of the storage management software and must be enabled
either by you or your storage vendor. The Volume Copy premium feature is used to
copy data from one volume (the source) to another volume (the target) in a single
storage array.
This feature can be used to back up data, to copy data from volume groups that use
smaller capacity drives to volume groups that use larger capacity drives, or to
restore snapshot volume data to the base volume. For detailed information on this
premium feature, refer to the Array Management Window online help or to the
SANtricity Storage Manager Volume Copy Feature Guide.
Source Volume
When you create a volume copy, a copy pair is created and consists of a source
volume and a target volume located on the same storage array. The source volume is
the volume that accepts host I/O and stores application data, and can be a standard
volume, snapshot volume, base volume of a snapshot volume, or a Remote Volume
Mirror primary volume.
Note – IMPORTANT If a primary volume is selected as the source volume for a
volume copy, you must ensure that the capacity of the target volume is equal to, or
greater than the usable capacity of the primary volume. The usable capacity for the
primary volume is the minimum of the primary and secondary volume's actual
capacities.
When a volume copy is started, data from the source volume is copied in its entirety
to the target volume. While the volume copy has a status of In Progress, Pending, or
Failed, the source volume is available for read I/O activity. After the volume copy is
completed, write requests are allowed to the source volume.