ONTAP 9.14

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Consistency groups overview

A consistency group is a collection of volumes that are managed as a single unit. In ONTAP, consistency groups provide easy management and a protection guarantee for an application workload spanning multiple volumes.

You can use consistency groups to simplify your storage management. Imagine you have an important database spanning twenty LUNs. You could manage the LUNs on an individual basis or treat the LUNs as a solitary dataset, organizing them into a single consistency group.

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

Learn about consistency groups

Consistency groups support any FlexVol volume regardless of protocol (NAS, SAN, or NVMe) and can be managed through the ONTAP REST API or in ONTAP System Manager under the Storage > Consistency Groups menu item. Beginning with ONTAP 9.14.1, consistency groups can be managed with the ONTAP CLI.

Consistency groups can exist as individual entities—​as a collection of volumes—​or in a hierarchical relationship, which consists of other consistency groups. Individual volumes can have their own volume-granular Snapshot policy. In addition, there can be a consistency group-wide Snapshot policy. The consistency group can only have one SnapMirror Business Continuity (SM-BC) relationship and shared SM-BC policy, which can be used to recover the entire consistency group.

The following diagram illustrates how you might use an individual consistency group. The data for an application hosted on SVM1 spans two volumes: vol1 and vol2. A Snapshot policy on the consistency group captures Snapshot copies of the data every 15 minutes.

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

Larger application workloads might require multiple consistency groups. In these situations, you can create hierarchical consistency groups, where a single consistency group becomes 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.

In the following example, an application is hosted on SVM1. The administrator has created a parent consistency group, SVM1_app, which includes two child consistency groups: SVM1appDataCG for the data and SVM1app_logCG for the logs. Each child consistency group has its own Snapshot policy. Snapshot copies of the volumes in SVM1appDataCG are taken every 15 minutes. Snapshots of SVM1app_logCG are taken hourly. The parent consistency group SVM1_app has an SM-BC policy which replicates the data to ensure continued service in the event of a disaster.

Diagram of a nested consistency group with its associated volumes

Beginning with ONTAP 9.12.1, consistency groups support cloning and modifying the members of the consistency by adding or removing volumes in both ONTAP System Manager and the ONTAP REST API. Beginning with ONTAP 9.12.1, the ONTAP REST API also supports:

  • Creating consistency groups with new NFS or SMB volumes or NVMe namespaces.

  • Adding new or existing NFS or SMB volumes or NVMe namespaces to existing consistency groups.

Monitor consistency groups

Beginning with ONTAP 9.13.1, consistency groups offer real-time and historical capacity and performance monitoring, offering insights about the performance of applications and individual consistency groups.

Monitoring data is refreshed every five minutes and is maintained for up to one year. You can track metrics for:

  • Performance: IOPS, latency, and throughput

  • Capacity: Size, logical used, available

You can view monitoring data in the Overview tab of the consistency group menu in ONTAP System Manager or by requesting it in the REST API. Beginning with ONTAP 9.14.1, you can view consistency group metrics with the CLI using the consistency-group metrics show command.

In ONTAP 9.13.1, you can only retrieve historical metrics using the REST API. Beginning with in ONTAP 9.14.1, historical metrics are also available in ONTAP System Manager.

Protect consistency groups

Consistency groups offer protection through:

Creating a consistency group does not automatically enable protection. Local and remote protection policies can be set when creating or after creating a consistency group.

To configure protection on a consistency group, see Protect a consistency group.

In order to utilize remote protection, you must meet the requirements for SnapMirror Business Continuity deployments.

SM-BC relationships cannot be established on volumes mounted for NAS access.

Consistency groups in MetroCluster configurations

Beginning with ONTAP 9.11.1, you can provision consistency groups with new volumes on a cluster within a MetroCluster configuration. These volumes are provisioned on mirrored aggregates.

After they are provisioned, you can move volumes associated with consistency groups between mirrored and unmirrored aggregates. Therefore, volumes associated with consistency groups can be located on mirrored aggregates, unmirrored aggregates, or both. You can modify mirrored aggregates containing volumes associated with consistency groups to become unmirrored. Similarly, you can modify unmirrored aggregates containing volumes associated with consistency groups to enable mirroring.

Volumes and Snapshot copies associated with consistency groups placed on mirrored aggregates are replicated to the remote site (site B). The contents of the volumes on site B provide a write-order guarantee for the consistency group, allowing you to recover from site B in the event of a disaster. You can access consistency group Snapshot copies using consistency group with the REST API and ONTAP System Manager on clusters running ONTAP 9.11.1 or later. Beginning with ONTAP 9.14.1, you can also access Snapshot copies with the ONTAP CLI.

If some or all the volumes associated with a consistency group are located on unmirrored aggregates that are not currently accessible, GET or DELETE operations on the consistency group behave as if the local volumes or hosting aggregates are offline.

Consistency group configurations for replication

If site B is running ONTAP 9.10.1 or earlier, only the volumes associated with the consistency groups located on mirrored aggregates are replicated to site B. The consistency group configurations are only replicated to site B, if both sites are running ONTAP 9.11.1 or later. After site B is upgraded to ONTAP 9.11.1, data for consistency groups on site A that have all their associated volumes placed on mirrored aggregates are replicated to site B.

It’s recommended you maintain at least 20% free space for mirrored aggregates for optimal storage performance and availability. Although the recommendation is 10% for non-mirrored aggregates, the additional 10% of space may be used by the filesystem to absorb incremental changes. Incremental changes increase space utilization for mirrored aggregates due to ONTAP’s copy-on-write Snapshot-based architecture. Failure to adhere to these best practices may have a negative impact on performance.

Upgrade considerations

Consistency groups created with SM-BC in ONTAP 9.8 and 9.9.1 will automatically be upgraded and become manageable under Storage > Consistency Groups in ONTAP System Manager or the ONTAP REST API when upgrading to ONTAP 9.10.1 or later. For more information about upgrading from ONTAP 9.8 or 9.9.1, see SM-BC upgrade and revert considerations.

Consistency group Snapshot copies created in the REST API can be managed through ONTAP System Manager’s Consistency Group interface and through consistency group REST API endpoints. Beginning with ONTAP 9.14.1, consistency group Snapshots can also be managed with the ONTAP CLI.

Snapshot copies created with the ONTAPI commands cg-start and cg-commit are recognized as consistency group Snapshots and thus cannot be managed through ONTAP System Manager’s consistency group interface or the consistency group endpoints in the ONTAP REST API. Beginning with ONTAP 9.14.1, these Snapshot copies can be mirrored to the destination volume if you are using an Asynchronous SnapMirror policy. For more information, see Configure asynchronous SnapMirror protection.

Supported features by release

ONTAP 9.14.1 ONTAP 9.13.1 ONTAP 9.12.1 ONTAP 9.11.1 ONTAP 9.10.1

Hierarchical consistency groups

Local protection with Snapshot copies

SnapMirror Business Continuity

MetroCluster support

Two-phase commits (REST API only)

Application and component tags

Clone consistency groups

Add and remove volumes

Create CGs with new NAS volumes


Create CGs with new NVMe Namespaces


Move volumes between child consistency groups

Modify consistency group geometry


Asynchronous SnapMirror (single consistency groups only)

SVM disaster recovery (single consistency groups only)

CLI support

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