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Configuring replication
20 Dell EMC SC Series: VMware Site Recovery Manager Best Practices | 2007-M-BP-V
5 Configuring replication
SC Series replication, in coordination with Site Recovery Manager (SRM), can provide a robust and scalable
disaster recovery solution. Since each replication method affects recovery differently, choosing the correct
method to meet business requirements is important. A brief summary of the different options is provided in
this section.
5.1 Asynchronous replication
In an asynchronous replication, the I/O must be committed to and acknowledged by the source system in
order for the data to be transferred to the destination in an independent timeframe. There are two different
methods to determine when data is transferred to the destination:
By snapshot schedule: The snapshot (replay) schedule dictates how often data is sent to the destination.
When each snapshot is taken, the SC Series system determines which blocks have changed since the last
snapshot (the delta changes), and then transfers them to the destination. Depending on the rate of change
and the bandwidth, it is entirely possible for the replications to fall behind, so it is important to monitor them
and verify that the recovery point objective (RPO) can be met.
Replicating the active snapshot: This method transfers data in near real time, which usually requires more
bandwidth than replicating only the delta changes in the snapshots. As each block of data is written on the
source volume, it is committed, acknowledged to the host, and then transferred to the destination as fast as
possible. Keep in mind that the replications can still fall behind if the rate of change exceeds available
bandwidth.
Asynchronous replications usually have more flexible bandwidth requirements making this the most common
replication method for organizations which allow an RPO requirement greater than zero (meaning some
amount of data will be lost when recovery from an asynchronous replication). Another benefit of
asynchronous replication is that the snapshots are transferred to the destination volume, allowing for
checkpoints at the source system as well as the destination system.
5.2 Synchronous replication
In a synchronous replication, data is replicated in real time to the destination. An I/O must be committed on
both systems before an acknowledgment is sent back to the host. This limits the type of links that can be
used, since they must be highly available with low latencies. High latencies across the link slow down access
times on the source volume.
5.3 QoS definitions
SRM supports replication from a source to a destination and can reverse the direction of replication after
recovery and reprotect plans have been invoked. As a best practice, maintain consistent QoS definitions on
each SC Series system in a replication pair to provide consistency and prevent unexpected replication
latency. Inconsistent QoS definitions between sites may also cause reprotect or failback workflows to fail.
5.4 Live Volume replication
Standard asynchronous replication or synchronous replication (either mode) can be leveraged by VMware
vSphere SRM protection groups, recovery plans, and reprotection. Live Volume replications add an