Asynchronous Storage Manager (ASM)

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The use of an ASM (or multiple ASMs) allows all database changes to be replicated to a remote passive data center without performance reduction caused by inter-datacenter delay in communication between remote locations. In the event of a disaster, a recent consistent snapshot of the database contents can be recovered and quickly put into service. The remote data center contains only Admin Processes (APs) and ASMs.

Redundant Storage Managers (SMs) running on independent physical hosts with their archives and journals on independent physical storage protect against single points of failure. However, with a massive multi-node failure due to natural disasters such as fire, hurricane, or earthquake, causing permanent destruction to the entire data center, all redundant SMs' archives will be lost. This may make the data center completely unavailable, or temporarily unavailable for longer than the acceptable maximum outage time. Without the use of ASMs, the database will have to be restored from a backup to new archives in a new data center. Restoring a large database from a backup can take a significant amount of time and the changes made since the most recent backup will be lost.

ASMs provide quicker disaster recovery with less data loss at the expense of additional hardware resources to run a remote data center. A remote data center should be sufficiently distant from the active data center such that a single disaster cannot disable both data centers.

The ASMs are located on the passive data center. They do not participate in NuoDB’s performance-sensitive network protocols executed inside the active data center. This prevents a database slowdown due to high latency of network communication between active and passive data centers. However, this might cause the loss of the most recently committed transactions during disaster recovery.

Periodic backups are recommended so you can undo unintended changes to the database by rolling back to a previous copy.