File System Replication

The Replication Process

The replication resource creates a special replication snapshot in the source file system. Then, it transfers the snapshot to the replication target resource, which writes the new data to the target file system. The last completed replication snapshot remains in both the source and target file system until the next interval. At the next interval, the replication process automatically deletes the old replication snapshots and creates a new one. The replication process continues to repeat at the specified interval as long as the replication is in effect.

In this diagram, File System A in the primary availability domain is replicated to File System B. The replication captures the delta of data written to File System A in a replication snapshot. Then, the data is transferred from the replication resource to the replication target resource, and copied to File System B.

If there's an outage in the primary (source) availability domain, you can fail over to the target file system. To fail over to the target file system, export it so applications and users can access it. See Disaster Recovery for more information.

Monitoring Replications and Outages

The File Storage service provides metrics so that you can track replication operations and potential outages. You can use metrics to analyze things like transfer between the source and target file systems, bandwidth, and metadata operations performed by the replication resource. For example, to monitor bandwidth issues and potential bottlenecks, you can monitor the total number of write operations on the source file system and the total data egress from the source file system to target file system. You can also use metrics to monitor the time between snapshot creation on the source file system and the time it's applied to the target. In this way you can determine how far the target file system is behind the source, and how much data would be lost if there's an outage. See File System Metrics and Overview of Monitoring.

Oracle recommends that you configure alarms on metrics like the error rate and latency in the source file system to indicate any impact to availability. You can also monitor OCI announcements and status dashboard for general service outages so that you can make necessary decisions about failover. Service outages don't always impact all customer resources equally, so it is very important that you determine your tolerances and put alarms in place. See Console Announcements and Events.

• Your tenancy must be subscribed to the destination region for cross-region replication. To subscribe to a region, see Managing Regions. See Recommended Target Regions for more information.
• When you enable cross-region replication for a file system, the process includes an initial sync of the data from the source file system to the target file system. Depending on the amount of data written to the file system, this sync can take hours. See Estimating Replication Time for more information.
• You can configure up to three replication jobs for each file system.
• The minimum replication interval is 60 minutes.
• You can't use replication to migrate data from an on-premises location to Oracle Cloud Infrastructure.
• Only a file system that has never been exported can be used as a target file system. To use a previously exported file system as a target, first create a clone of the file system. Then, you can use the clone as a target.
• If you create or delete user snapshots on a file system, you can't use that file system as a target file system for replications, even if you haven't exported the file system.
• A file system with a snapshot policy attached can't be used as a target file system.
• If you delete a replication resource, replication snapshots on the target file system are converted to user snapshots. If you delete one of these snapshots, you can't reuse the target file system as a target file system for future replications.

Cost Considerations for Replication

After you enable replication for a file system, the file system is replicated to a target file system in the specified region and availability domain. File Storage is metered for total capacity stored on disk for both the source and target file systems. Source and target file systems are priced at the same rate. See File System Usage and Metering for more information.

Your bill includes any applicable network costs for the replication process between regions. As part of the replication process, all data being updated on the source file system is transferred to the file system replica, so file systems with continual updates incur higher network costs. There is no additional charge for cross-availability domain bandwidth within the same region or inbound data transfer.

Many replication scenarios use a clone of an original source or target file system. Cloning the source from the last completely applied snapshot ensures that the source and target are compatible. You can also choose to use a new file system for failback. However, using a clone of the original source file system tends to be both faster and more cost effective than using a new file system. See Clone Metered Utilization for more information about metering and billing for clones. See Replication Metered Utilization for detailed examples of metering for file systems, snapshots, and clones as they're used in replication.

Recommended Target Regions

When you enable replication for a file system and create a new target file system, you select a region to replicate to. The source region for the file system determines the recommended target regions available as a destination region for replication in the Console. Most regions have one or more regions available as recommended destination regions. Recommended target regions are selected based on geographical locations to maximize performance. If you need to replicate a file system to a region that's not recommended, you can create a target file system for replication in that region, or use the API or CLI.

The following table lists the recommendations for the Oracle Cloud Infrastructure commercial realm. To subscribe to a region, see Managing Regions.