asynchronous replication

What is asynchronous replication?

Asynchronous replication is a store-and-forward approach to backup and data protection.

Asynchronous replication writes data to the primary storage array first, and then, depending on the implementation approach, commits data to be replicated to memory or a disk-based journal. It then copies the data in real time or at scheduled intervals to replication targets.

Synchronous vs. asynchronous replication

The primary difference between synchronous replication and asynchronous replication is the way in which data is written to the replica. Most synchronous replication products write data to primary storage and the replica simultaneously. The primary copy and the replica should always remain synchronized.

In contrast, asynchronous replication products write data to the primary storage first and then copy the data to the replica. Although the replication process can occur in near real time, it is more common for replication to occur on a scheduled basis. For instance, write operations might be transmitted to the replica in batches on a periodic basis.

The benefits of asynchronous replication

There are two main benefits to asynchronous replication:

• It tends to cost significantly less than synchronous replication. Synchronous replication requires more bandwidth than asynchronous replication and might also require specialized hardware, depending on the implementation.
• It is designed to work over long distances. Since the replication process does not have to occur in real time, asynchronous replication can tolerate some degradation in connectivity.

Synchronous replication is typically used to provide high availability of critical applications. In this scenario, failover from the primary to secondary array is nearly instantaneous, to ensure little to no application downtime.

Asynchronous replication use cases

A variety of data replication tools are available. Asynchronous replication is commonly used in data backups. These backups can be local, but the technology is frequently used for off-site backups. Cloud backups also use asynchronous replication.

Some enterprise-grade hypervisors include an asynchronous replication feature that allows entire virtual machines to be replicated to a remote location so that VMs can fail over to that location in the event of a disaster. This is commonly referred to as instant recovery or recovery-in-place, and a number of backup software products support this functionality. Asynchronous replication is also frequently used with storage snapshots for continuous data protection.