HP MSA 1040 HP MSA 1040 SMU Reference Guide (762784-001, March 2014) - Page 122

associated with the standard snapshot and there is no data specifically associated with the replication snapshot. If

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Figure 4 Intersite and intrasite replication sets Remote replication uses snapshot functionality to track the data to be replicated and to determine the differences in data updated on the master volume, minimizing the amount of data to be transferred. In order to perform a replication, a snapshot of the primary volume is taken, creating a point-in-time image of the data. This point-in-time image is then replicated to the secondary volume by copying the data represented by the snapshot using a transport medium such as TCP/IP (iSCSI) or Fibre Channel. The first replication copies all data from the primary volume to the secondary volume; subsequent replications use sparse snapshots. A sparse snapshot stores only those blocks that are different from an already existing full copy of the data. Replication snapshots are retained for both the primary volume and the secondary volume. When a matching pair of snapshots is retained for both volumes, the matching snapshots are referred to as replication sync points. The two snapshots (one on each volume) are used together as a synchronization reference point, minimizing the amount of data to transfer. The two snapshots in a replication sync point are assigned the same image ID, which uniquely identifies that the data in those snapshots are from the same point-in-time image and are block-for-block identical. When a replication snapshot is created from a standard snapshot, while that snapshot remains present the replication snapshot's total data represented is zero bytes. This behavior occurs because the snapshot data remains associated with the standard snapshot and there is no data specifically associated with the replication snapshot. If the standard snapshot is deleted, its data becomes associated with (is preserved by) the replication snapshot and the replication snapshot's size changes to reflect the size of the deleted snapshot. An added benefit of using snapshots for replication is that these snapshots can be kept and restored later in the event of a non-hardware failure, such as virus attack. Since the replication source is a snapshot, any writes performed on the primary volume after the snapshot is taken are not replicated by that task. This gives you more control over what is contained in each replication image. NOTE: Because replication is not synchronous (continuous), data in a secondary volume is only as current as the last replication that completed successfully. Replications can be performed manually or scheduled. 122 Using Remote Snap to replicate volumes

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122
Using Remote Snap to replicate volumes
Figure 4
Intersite and intrasite replication sets
Remote replication uses snapshot functionality to track the data to be replicated and to determine the differences in
data updated on the master volume, minimizing the amount of data to be transferred.
In order to perform a replication, a snapshot of the primary volume is taken, creating a point-in-time image of the
data. This point-in-time image is then replicated to the secondary volume by copying the data represented by the
snapshot using a transport medium such as TCP/IP (iSCSI) or Fibre Channel. The first replication copies all data from
the primary volume to the secondary volume; subsequent replications use sparse snapshots. A sparse snapshot stores
only those blocks that are different from an already existing full copy of the data.
Replication snapshots are retained for both the primary volume and the secondary volume. When a matching pair of
snapshots is retained for both volumes, the matching snapshots are referred to as
replication sync points
. The two
snapshots (one on each volume) are used together as a synchronization reference point, minimizing the amount of
data to transfer. The two snapshots in a replication sync point are assigned the same
image ID
, which uniquely
identifies that the data in those snapshots are from the same point-in-time image and are block-for-block identical.
When a replication snapshot is created from a standard snapshot, while that snapshot remains present the
replication snapshot’s total data represented is zero bytes. This behavior occurs because the snapshot data remains
associated with the standard snapshot and there is no data specifically associated with the replication snapshot. If
the standard snapshot is deleted, its data becomes associated with (is preserved by) the replication snapshot and the
replication snapshot’s size changes to reflect the size of the deleted snapshot.
An added benefit of using snapshots for replication is that these snapshots can be kept and restored later in the event
of a non-hardware failure, such as virus attack. Since the replication source is a snapshot, any writes performed on
the primary volume after the snapshot is taken are not replicated by that task. This gives you more control over what
is contained in each replication image.
NOTE:
Because replication is not synchronous (continuous), data in a secondary volume is only as current as the last
replication that completed successfully. Replications can be performed manually or scheduled.