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30 PS Series Asynchronous Replication Best Practices and Sizing Guide | BP1012
Figure 13 shows the remote replicas that are available for a volume as displayed in Group Manager from the
primary group. In this case, there are five replicas of a volume on the remote storage system. The number of
replicas retained on the remote partner system is determined by the size of the volumes being replicated and
the amount of changed data that is replicated, the size of the replica reserve, and the delegated space. The
total size of all replicas cannot exceed the total replica reserve space available (in Figure 13, 840 GB is
allocated).
Navigation tip: Group Manager GUI (primary) > Replication > Outbound Replicas > select volume
Outbound replicas for repl-vol1 on the PrimaryGroup
7.5 Initial capacity planning and sizing example
For the initial sizing of a solution for PS Series storage, the concepts described in this document may be more
easily understood with a real-world example. Best practice sizing techniques are by design conservative
enough to account for the needed space on the primary and secondary. The local replication reserve should
also be large enough to handle the in-flight replications, as well as the initial volume capacity. The secondary
will need similar space considerations.
So for a simple and conservative rule, 200 percent of the space per volume should be allocated on the
secondary delegated space as well as the primary local replication reserve. This is not a hard and fast rule
and the space efficient approach may be taken as indicated in Table 4. However, to arrive at the correct
future change rate, detailed analysis and understanding of the applications, growth, and business needs
should be considered carefully. The approach presented here will use the more conservative approach to
avoid under sizing the solution.
Since replication is at the volume level, we will demonstrate how to size the volumes which will replicate from
the primary to a selected secondary group and pool. The pool will need enough space to hold the total of all
replicas of the volumes replicating to this secondary group. If replication schedules are used then the number
of replicas to retain will also need to be considered.