Bucket Replication

Resynchronization (Disaster Recovery)

Resynchronization primarily supports recovery after partial or total loss of the data on a MinIO deployment using a healthy deployment in the replica configuration. Use the mc replicate resync command completely resynchronize the remote target (mc admin bucket remote) using the specified source bucket.

The resynchronization process checks all objects in the source bucket against all configured replication rules that include existing object replication. For each object which matches a rule, the resynchronization process places the object into the replication queue regardless of the object’s current replication status.

MinIO skips synchronizing those objects whose remote copy exactly match the source, including object metadata. MinIO otherwise does not prioritize or modify the queue with regards to the existing contents of the target.

mc replicate resync operates at the bucket level and does not support prefix-level granularity. Initiating resynchronization on a large bucket may result in a significant increase in replication-related load and traffic. Use this command with caution and only when necessary.

For buckets with object transition (Tiering) configured, replication resynchronization restores objects in a non-transitioned state with no associated transition metadata. Any data previously transitioned to the remote storage is therefore permanently disconnected from the remote MinIO deployment. For tiering configurations which specify an explicit human-readable prefix as part of the remote configuration, you can safely purge the transitioned data in that prefix to avoid costs associated to the “lost” data.

Replication of Delete Operations

MinIO supports replicating delete operations, where MinIO synchronizes deleting specific object versions and new delete markers. Delete operation replication uses the same replication process as all other replication operations.

MinIO requires explicitly enabling versioned deletes and delete marker replication . Use the mc replicate add --replicate field to specify both or either delete and delete-marker to enable versioned deletes and delete marker replication respectively. To enable both, specify both strings using a comma separator delete,delete-marker.

For delete marker replication, MinIO begins the replication process after a delete operation creates the delete marker. MinIO uses the X-Minio-Replication-DeleteMarker-Status metadata field for tracking delete marker replication status. In active-active replication configurations, MinIO may produce duplicate delete markers if both clusters concurrently create a delete marker for an object or if one or both clusters were down before the replication event synchronized.

For replicating the deletion of a specific object version, MinIO marks the object version as PENDING until replication completes. Once the remote target deletes that object version, MinIO deletes the object on the source. While this process ensures near-synchronized version deletion, it may result in listing operations returning the object version after the initial delete operation. MinIO uses the X-Minio-Replication-Delete-Status for tracking delete version replication status.

MinIO only replicates explicit client-driven delete operations. MinIO does not replicate objects deleted from the application of lifecycle management expiration rules. For active-active configurations, set the same expiration rules on all of of the replication buckets to ensure consistent application of object expiration.

Replication of Existing Objects

MinIO by default replicates existing objects in the source bucket to the configured remote, similar to AWS: Replicating existing objects between S3 buckets without the overhead of contacting technical support.

MinIO marks all objects or object prefixes that satisfy the replication rules as eligible for synchronization to the remote cluster and bucket. MinIO only excludes those objects without a version ID, such as those objects written before enabling versioning on the bucket.

You can disable existing object replication while configuring or modifying the bucket replication rule. You must specify all desired replication features during creation or modification:

• For new replication rules, exclude "existing-objects" from the list of replication features specified to mc replicate add --replicate.

• For existing replication rules, remove "existing-objects" from the list of existing replication features using mc replicate update --replicate. The new rule replaces the previous rule.

Disabling existing object replication does not remove any objects already replicated to the remote bucket.

Synchronous vs Asynchronous Replication

MinIO supports specifying either asynchronous (default) or synchronous replication for a given remote target.

With asynchronous replication, MinIO completes the originating PUT operation before placing the object into a replication queue. The originating client may therefore see a successful PUT operation before the object is replicated. While this may result in stale or missing objects on the remote, it mitigates the risk of slow write operations due to replication load.

With synchronous replication, MinIO attempts to replicate the object prior to completing the originating PUT operation. MinIO returns a successful PUT operation whether or not the replication attempt succeeds. This reduces the risk of slow write operations at a possible cost of stale or missing objects on the remote location.

You must explicitly enable synchronous replication when configuring the remote target target using the mc admin bucket remote add command with the add flag.

Replication Internals

This section documents internal replication behavior and is not critical to using or implementing replication. This documentation is provided strictly for learning and educational purposes.