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10 Using Dell PS Series Asynchronous Replication | TR1052
2.3 Volumes
Up to 128 volumes per group can be configured for replication (and active replication) at any time. A
volume can have only one replication partner. However, different volumes on the same PS Series group
can replicate to different partners.
For example, on GroupA, the replication partners are GroupB and GroupC. On GroupA, the volumes and
their replication partners can be set up in the following example:
 Vol1  GroupB
 Vol2 and Vol3  GroupC
2.4 Volume collections
A volume collection is a group of up to eight volumes that can be managed together. For example, a
volume collection can consist of: a volume for a database and another volume for its log file, volumes that
store email, volumes for a particular group of users or a department, or any other volumes that you want
to replicate at the same time. All volumes in a collection must be configured to replicate to the same
partner.
2.5 Replica frequency and keep count
Each volume can have up to 512 replicas stored on its partner.
Based on your RTO and RPO, you can specify how often to replicate a volume and how many replicas you
want to keep on the partner group.
For example, if your volume data does not often change, you might decide to replicate the volume once
per week. Depending on how much data is replicated each time and the amount of replica reserve, you
could keep, for example, many weeks' or months' worth of replicas on the partner.
On the other hand, if the data of a volume changes frequently and you want to minimize the amount of
potential transaction loss in the event of a disaster, you might decide to replicate the volume daily or even
hourly. For example, you could keep a full day’s worth of hourly replicas on the partner.
The replication frequency and the number of replicas to keep depend on your business needs, and are
limited only by the configuration limits and the amount of space available on the volume’s replication
partner.
Use the following formula to determine the number of replicas to keep:
Frequency of replications x time period to retain = Number of replicas to keep
For example: 2 replications per day x 14 days = 28 replicas
Note: A group can have up to 10,000 snapshots and replicas (total) from all of its replication partners.