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

About the Remote Snap replication feature 123
NOTE: 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.
Replication actions
The following figure illustrates actions that occur during a series of replications from System 1 to System 2.
Figure 5 Actions that occur during a series of replications
The figure above illustrates initial, delta, and queued replications:
• Initial replication: When the first replication is initiated, a snapshot of the primary volume is taken and every
block of data is then copied to the secondary volume. When the copy is complete, the first snapshot is taken on
the secondary volume, creating the first sync point. This sync point can be used to determine the delta data from
that sync point to a later snapshot. Actions 1–4 are the initial replication.
1 Take initial snapshot and initiate replication.
2 Initial replication consists of a full data copy.
3 Take second snapshot and request replication. This
can be taken while the initial replication is in progress.
4 Snapshot taken on secondary volume. This is the first
replication sync point.
5 When the initial replication is complete, the second
replication automatically starts. Only the data
changed since Snap 1 is replicated.
6 Second snapshot taken on secondary volume. This is
the second sync point.
7 Other snapshots can be taken and replication initiated
on the primary volume while replication is in progress.
These snapshots are queued waiting for prior
replications to complete. These replication snapshots
will not become sync points until their replications are
complete.