A. SCR isn't limited to one source and one target. For each source, you can have multiple SCR targets on different servers, and each SCR target server can contain SCR replicas from different source servers, so you have a lot of flexibility in your configuration. The best practice is to have no more than four targets for each SCR source, but this isn't a hard limit.
The SCR source server can be a standalone server (with or without LCR) or a clustered mailbox server using CCR or SCC (making sure there's only one database per storage group).
The SCR target server can be a standalone mailbox server (but can't have LCR enabled for any storage groups) or a node in a failover cluster where the mailbox role is installed but no clustered mailbox server is configured on the cluster (essentially, an Exchange empty cluster with only the role installed).
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