Slowdowns often plague enterprises that use mirroring or replication for high availability or disaster recovery between locations. If you have many locations or many database tables -- or a lot of transactions or journaling that needs to stay in sync between multiple locations -- watch out, because the performance loss can be dramatic.
If possible, run your mirroring and replication activity across separate WAN “pipes” to keep it isolated from production traffic. Your network design team can assist with a viable topology. At the same time, go over the configuration (star topology, for example) you intend to use to support mirroring and replication. Vendor representatives and the network design team can provide useful input on constructing a configuration that will prevent network saturation.
Configuration aside, mirroring and replication products -- such as XOsoft’s WANSyncHA Oracle or High Availability Linux Project’s Heartbeat -- usually provide options to control timing and traffic flow between sites. Some products enable you to schedule syncing activity during off hours, whereas others let you activate syncing tasks only if a particular threshold is reached. Use those controls; that’s what they’re there for.