About instance replication

Filestore now offers asynchronous replication for your instances.

A source instance can be continuously and asynchronously replicated to a standby instance in a location of your choice.

To select customers, Filestore offers instance replication support for instances created in the following service tiers:

  • Zonal
  • Regional
  • Enterprise

Instance replication compared to other data recovery options

The following sections cover the advantages of instance replication compared to snapshots and backups.

Snapshots

Snapshots are resources that consume capacity within the instance and allow you to revert the current state of your instance data to a previous, specific point in time. Users can also elect to revert to a previous version of a specific file.

Snapshots don't replicate any data or consume capacity until the data on the instance is modified. All snapshots of an instance share in-common data, meaning that the instance preserves only the differences between the snapshots.

While snapshots do offer cost efficiency when compared to other Filestore data recovery operations, available instance capacity continuously decreases as file modifications are made.

Reverting an instance to a previous state is destructive, as it deletes the latest version of instance data, and should be used carefully.

Backups

Backups are external resources that reside outside of the instance, consuming their own separate capacity. The first backup is a complete copy of instance data, with each subsequent backup only consuming the data necessary to track incremental and differential changes since the previous backup. Internally, a backup chain's history is tracked using snapshots, which consume capacity on the source instance.

Instance replication

Instance replication pairs a source instance with a replica instance, a separate resource in a secondary location that continuously monitors any changes made to the source and asynchronously replicates those changes to the replica instance within a target recovery point objective (RPO) of approximately 30 minutes.

This process relies on snapshots and similarly consumes capacity. As snapshots become obsolete, they are deleted to free up instance capacity in both instances.

The replica instance is a continuously updated, complete copy of the source instance. Most copies are scheduled every five to ten minutes. Metrics are available indicating the timestamp of the last full instance copy. For more information, see Monitoring.

Instance pair roles

When instance replication is enabled, each instance in the pair is assigned a role:

  • ACTIVE

    The source instance.

  • STANDBY

    The replica instance.

Role changes are not automatic and can only be initiated by the user.

Promote replica

While the replica instance can't be mounted or written to directly, in the event of a service outage, the replica can perform a promote-replica operation. This same operation is accessible from the Google Cloud console.

This operation initiates the following actions:

  • Stops replication between the ACTIVE and STANDBY instances.
  • Unpairs the two resources.
  • Promotes the replica to a regular instance that is capable of client connections and writes just as any other instance.
  • The replication role, whether ACTIVE or STANDBY, is removed from both instances.
  • When the operation successfully completes, the replica instance's state changes from PROMOTING to READY.

Once your application is back online, this new source instance can then be paired with a new replica and you can initiate instance replication once again.

To see how to run the operation, see Break replication.

Failback

The promote-replica operation initiates a break in replication. It is a switchover not a failover event, meaning that failback isn't automatic. Once the operation is complete, administrators must reconnect their applications to the new source instance.

Limitations

The following limitations apply:

  • Not available in the following service tiers:

    • Basic HDD
    • Basic SSD

  • The following specifications must be the same for each instance in the pair:

The following sections cover other feature limitations related to RPO, operations, network traffic, performance, and availability in detail:

RPO

  • Quoted RPO times are approximate and not supported under any Filestore service level agreement (SLA).

  • The target 30-minute RPO applies to instances with a change rate of 100 MB per second and an IOPS rate of 300 per second, where IOPS are defined as any create, edit, or delete operation applied to any file or directory.

    Instances with a higher change rate may experience longer replication periods. RPO times vary and don't strictly map linearly with higher change rates. For example, if the change rate doubles, the RPO window won't necessarily double.

  • Instance replication is specified at instance creation. If you want to pair a replica with a source instance, you must enable instance replication on the instance when creating it, and then pair it with the replica. An existing instance can't be used as a replica.

Operations

  • The following operations are disabled on the ACTIVE instance:

    • Instance deletion
    • Revert to snapshot

  • The following limitations apply to the STANDBY instance:

    • Doesn't support NFS access
    • Backups are disabled
    • Snapshots are disabled

Network traffic

  • Continuous data replication between the source and replica instances accrues network traffic fees. For more information, see Filestore pricing or your Filestore representative.

Performance

  • Continuous data replication between the pair impacts IOPS performance on the source instance.

Availability

  • Some restrictions apply when choosing a region for your replica instance. For more information, see your Filestore representative.

  • Deleting the source instance won't delete its associated replica. If the source instance no longer exists, and you want to delete the instance previously used as its replica, use gcloud to locate and delete the instance.

Recommendations

For a robust disaster recovery solution, users are strongly encouraged to choose a separate region rather than a separate zone for the replica instance.

Monitoring

The time_since_last_replication metric represents the timestamp of the last full copy of the active instance.

For more information, see the following resources:

Pricing

When you use instance replication, charges for instances and cross-region networking apply. Replicating instances is offered at no additional charge. The replica instance is a continuously updated, complete copy of the source instance. Pricing is commensurate with the data recovery support provided in a continuous data recovery option suitable for enterprise workloads.

For more information, see your Filestore representative.

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