Consistency groups overview

Contributors

A consistency group is a collection of volumes that provides a write-order consistency guarantee for an application workload spanning multiple volumes.

Consistency groups facilitate application workload management, providing easy management of local and remote protection policies and providing simultaneous crash-consistent or application-consistent Snapshot copies of a collection of volumes at a point in time. Snapshots in consistency groups enable an entire application workload to be restored.

Consistency groups support any FlexVol volume regardless of protocol (NAS, SAN, or NVMe) and can be managed through the ONTAP REST APIs or in System Manager under the Storage > Consistency Groups menu item.

Consistency groups can exist on their own or in a hierarchical relationship. An individual consistency group is a collection of volumes. Volumes can individual or shared local Snapshot policies. The consistency group can only have one shared SM-BC policy, which can be used to recover the entire consistency group.

Diagram of a single consistency group with its consituent volumes and local Snapshot policy

Larger application workloads may require multiple consistency groups. In these situations, multiple consistency groups can be placed together in a hierarchical relationship. In this configuration, single consistency groups become the child components of a parent consistency group. The parent consistency group can include up to five child consistency groups. Like in individual consistency groups, a remote SM-BC protection policy can be applied to the entire configuration of consistency groups (parent and children) to recover the application workload.

Diagram of a nested consistency group with its consituent volumes

Protection

Consistency groups offer remote protection through SnapMirror Business Continuity (SM-BC) and local protection through Snapshot policies. In order to utilize remote protection, you must meet the requirements for SnapMirror Business Continuity deployments. By default, consistency groups do not have a protection policy set and will not protect your data unless a policy is selected. See “Protect a consistency group” for more information.

Upgrade considerations

Consistency groups created with SM-BC in ONTAP 9.8 and 9.9 will automatically be upgraded and become manageable under Storage > Consistency Groups in System Manager or the ONTAP REST API when upgrading to ONTAP 9.10.1. For more information about upgrading, see SM-BC upgrade and revert considerations.

Consistency group snapshots created with the ONTAP REST API can be managed through System Manager’s Consistency Group interface and through consistency group API endpoints.

Snapshots created with the ONTAPI commands cg-start and cg-commit will not be recognized as consistency group Snapshots and thus cannot be managed through System Manager’s Consistency Group interface or the consistency group endpoints in the ONTAP API.

Consistency group object limits

Consistency Groups

Scope

Minimum

Maximum

Number of consistency groups

Cluster

0

Same as maximum volume count in cluster

Number of parent consistency groups

Cluster

0

Same as maximum volume count in cluster

Number of individual and parent consistency groups

Cluster

0

Number of volumes in a consistency group

Consistency group

Same as maximum volume count in cluster

1

80

Number of volumes in the child of a parent consistency group

Parent consistency group

1

80

Number of volumes in a child consistency group

Child consistency group

1

80

Number of child consistency groups in a parent consistency group

Parent consistency group

1

5

If you are using SM-BC, refer to SM-BC restrictions and limitations for limits.