Replication Topology is a design for copying data between servers to protect against failures. In Azure, this manages copying data for both on-premises physical machines and Azure virtual machines (VMs). The goal is to provide high availability and disaster recovery for Windows Server environments, ensuring business can continue even if a server or site goes down.
The process begins by creating a central management point called a Recovery Services vault in Azure, which stores recovery points. You then create replication policies that define how often data is copied and how recovery points are kept. Finally, you enable replication for each server, which automatically installs a helper service called the Mobility service to handle the data transfer.
A key decision is choosing how data is copied between locations. Synchronous replication writes data to both the source and target at the same time. This guarantees no data loss but can slow performance because it waits for both writes to finish. Asynchronous replication writes data locally first and then copies it afterward, which is faster but means the target might be slightly behind the source. Choosing the right method helps you meet your Recovery Point Objective (RPO), which is the maximum amount of data loss your business can tolerate.
When you need to switch operations to the backup site, you perform a failover. A planned failover is used for maintenance or migrations. It ensures no data loss by first fully synchronizing the source and target before making the switch. An unplanned failover is for emergencies like a disaster. It uses the last synchronized data, which might mean some recent data is lost, depending on your replication schedule. After any failover, you must validate that applications and data are working correctly on the new server to ensure continuity.
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Synchronous replication writes data to both the source and target at the same time, guaranteeing no data loss but potentially slowing performance. Asynchronous replication writes data locally first and then copies it afterward, which is faster but means the target might be slightly behind the source.
A Recovery Services vault in Azure serves as a central management point that stores recovery points for replication. It is part of the process for setting up replication policies and enabling replication for servers.
A planned failover is used for maintenance or migrations and ensures no data loss by first fully synchronizing the source and target. An unplanned failover is for emergencies like a disaster and uses the last synchronized data, which might mean some recent data is lost.