Learn about ONTAP data protection fan-out and cascade deployments
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You can use a fan-out deployment to extend data protection to multiple secondary systems. You can use a cascade deployment to extend data protection to tertiary systems.
Both fan-out and cascade deployments support any combination of SnapMirror DR, SnapVault, or unified replication. Beginning with ONTAP 9.5, SnapMirror synchronous relationships support fan-out deployments with one or more SnapMirror asynchronous relationships. Only one relationship in the fan-out configuration can be a SnapMirror synchronous relationship, all the other relationships from the source volume must be SnapMirror asynchronous relationships. SnapMirror synchronous relationships also support cascade deployments (beginning with ONTAP 9.6); however, the relationship from the destination volume of the SnapMirror synchronous relationship must be a SnapMirror asynchronous relationship. SnapMirror active sync (supported beginning with ONTAP 9.13.1) also supports fan-out configurations.
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You can use a fan-in deployment to create data protection relationships between multiple primary systems and a single secondary system. Each relationship must use a different volume on the secondary system. |
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You should be aware that volumes that are part of a fan-out or cascade configuration can take longer to resynchronize. It is not uncommon to see the SnapMirror relationship reporting the status "preparing" for an extended time period. |
How fan-out deployments work
SnapMirror supports multiple-mirrors and mirror-vault fan-out deployments.
A multiple-mirrors fan-out deployment consists of a source volume that has a mirror relationship to multiple secondary volumes.
A mirror-vault fan-out deployment consists of a source volume that has a mirror relationship to a secondary volume and a SnapVault relationship to a different secondary volume.
Beginning with ONTAP 9.5, you can have fan-out deployments with SnapMirror synchronous relationships; however, only one relationship in the fan-out configuration can be a SnapMirror synchronous relationship, all the other relationships from the source volume must be SnapMirror asynchronous relationships.
How cascade deployments work
SnapMirror supports mirror-mirror, mirror-vault, vault-mirror, and vault-vault cascade deployments.
A mirror-mirror cascade deployment consists of a chain of relationships in which a source volume is mirrored to a secondary volume, and the secondary volume is mirrored to a tertiary volume. If the secondary volume becomes unavailable, you can synchronize the relationship between the primary and tertiary volumes without performing a new baseline transfer.
In a relationship of cascaded volumes, long-term retention (LTR) snapshots are supported only on the final SnapMirror destination volume of the cascade in all versions of ONTAP 9. Enabling LTR snapshots on any middle volume in the cascade results in missed backups and snapshots. If you have an unsupported configuration in which LTR snapshots have been enabled on any middle volume of a cascade, contact technical support and reference Knowledge Base article Cascading a volume with Long-Term Retention (LTR) snapshots enabled is not supported for assistance.
The following ONTAP versions do not allow you to enable LTR snapshots on any volume in a cascade except the final SnapMirror destination volume.
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9.15.1 and later
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9.14.1P2 and P4-P14
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9.13.1P9-P17
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9.12.1 P12-P19
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9.11.1P15-P20
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9.10.1P18-P20
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9.9.1P20
Learn more about long-term retention snapshots.
Beginning with ONTAP 9.6, SnapMirror synchronous relationships are supported in a mirror-mirror cascade deployment. Only the primary and secondary volumes can be in a SnapMirror synchronous relationship. The relationship between the secondary volumes and tertiary volumes must be asynchronous.
A mirror-vault cascade deployment consists of a chain of relationships in which a source volume is mirrored to a secondary volume, and the secondary volume is vaulted to a tertiary volume.
Vault-mirror and vault-vault cascade deployments are also supported:
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A vault-mirror cascade deployment consists of a chain of relationships in which a source volume is vaulted to a secondary volume, and the secondary volume is mirrored to a tertiary volume.
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A vault-vault cascade deployment consists of a chain of relationships in which a source volume is vaulted to a secondary volume, and the secondary volume is vaulted to a tertiary volume.