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What are the SnapMirror policy types and what do they mean?

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Applies to

  • Clustered Data ONTAP 8.3 
  • ONTAP 9 

Answer

SnapMirror policy types were introduced starting in clustered Data ONTAP 8.3 for Version-Flexible (also known as Unified Replication in ONTAP 9 and later) SnapMirror relationships. These policy types have a significant effect on the behavior of SnapMirror relationships and allow for greater flexibility when choosing what data is to be replicated and retained. Additional default policies have also been created to use the new policy types.

Policy Type Definition
async-mirror Behaves similarly to DP mirrors. This policy type does not support rules with user-defined Snapshot labels. It only allows two predefined labels
sm_created & all_source_snapshots The policy rules support only two combinations of these labels, either just sm_created or both sm_created and all_source_snapshots. 

mirror-vault

Allows for both DR and Vaulting into the same volume. Replicates the active file system of the Source to the Destination and allows the Destination to retain data for a longer retention period. Data is replicated with either the sm_created or system-defined / custom rules and is retained for a longer duration with user-defined rules based of user-defined Snapshot labels. 
vault Vaults and backups only. This policy type is what defines a relationship as a SnapVault rather than a Version-Flexible SnapMirror.
sync-mirror & strict-sync-mirror These policy types are used for synchronous Disaster Recovery and are supported only by Extended Data Protection (XDP) relationships between FlexVol volumes. All writes to the primary are replicated to the secondary before the write is acknowledged to the client. The strict-sync-mirror variant restricts further client IO on the primary upon a replication failure, whereas the sync-mirror variant does not. These policy types do not support replication of user Snapshot copies

Default policies:

clusterA::> snapmirror policy show
Vserver Policy             Policy Number         Transfer
Name    Name               Type   Of Rules Tries Priority Comment
------- ------------------ ------ -------- ----- -------- ----------
clusterA
        DPDefault          async-mirror  1     8  normal  Default policy for DP relationship.
  SnapMirror Label: sm_created                         Keep:       1
                                                 Total Keep:       1
 
clusterA
        MirrorAllSnapshots async-mirror  2     8  normal  Asynchronous SnapMirror policy for mirroring all snapshots and the latest active file system.
  SnapMirror Label: sm_created                         Keep:       1
                    all_source_snapshots                           1
                                                 Total Keep:       2
 
clusterA
        MirrorAndVault     mirror-vault  3     8  normal  A unified Asynchronous SnapMirror and SnapVault policy for mirroring the latest active file system and daily and weekly snapshots.
  SnapMirror Label: sm_created                         Keep:       1
                    daily                                          7
                    weekly                                        52
                                                 Total Keep:      60
 
clusterA
        MirrorLatest       async-mirror  1     8  normal  Asynchronous SnapMirror policy for mirroring the latest active file system.
  SnapMirror Label: sm_created                         Keep:       1
                                                 Total Keep:       1
 
clusterA
        XDPDefault         vault         2     8  normal  Default policy for XDP relationship with daily and weekly rules.
  SnapMirror Label: daily                              Keep:       7
                    weekly                                        52
                                                 Total Keep:      59

 

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