Consistency groups

A consistency group is a set of volumes that can be used to create a point in time snapshots, or to create a consistency copy of volumes. PowerVC consistency groups feature uses OpenStack generic volume group APIs.

Users with Administrator or Storage manager role can create consistency groups, and group snapshots.

For creating consistency group, a group type must exist. Group type is used to categorize a group just as storage template is used to describe the volume properties. However, they are common across multiple storage drivers. Post installation, PowerVC creates the default group types, which can be used for consistency group creation.
  • default_grouptype: Used to create consistency group and consistency group snapshots. This group type has consistent_group_snapshot_enabled property enabled.
  • default_grouptype_with_replication: Used with volume with replication properties. This group type has consistent_group_replication_enabled property, which allows consistency group creation for replicated volumes.
  • default_group_type_grs: Default group type for Global Replication Services API, used internally by PowerVC for APIs. GUI support is not available for this group type.

You can create additional group types from the GUI. PowerVC also has an additional group type "replication_enabled_vmrm. Use this group type when using PowerVC with VM Recovery Manager for IBM® Storwize® volumes in Global Mirror relationship Global mirror with VM Recovery Manager (VMRM) for High Availability (HA).

Working with consistency groups

Consider the following when working with consistency groups.
  • Volume can be part of only a single consistency group.
  • Consistency group can be created only for volumes from a single storage provider.
  • You can create consistency group for both available and in-use volumes.
  • Volume with replication enabled should use the replication group type.
  • On successful creation of consistency group, it can be used to create Group Snapshot. Group snapshot creates volume snapshots for volumes, which are part of a snapshot group.
  • You can also create consistency group, by selecting an existing consistency group. To do this use PowerVC Clone icon. Cloning a consistency group is only allowed for consistency group with volumes in available state. If consistency group has an in-use volume, then create a group snapshot and then use that for creating consistency group.
  • You can add or remove volumes from a consistency group. Maximum number of volumes which can added in consistency group depends on the storage driver specification.
    Note: PowerMax does not allow to add or remove volumes from a consistency group, if a group snapshot exists.
  • When a group snapshot is deleted, it also deletes the associated volume snapshots.
  • When consistency group is deleted, it also deletes the volumes, which are part of the consistency group. Before deleting a consistency group ensure that there are no associated group snapshots.
  • If a virtual machine or a volume with consistency group or a consistency group snapshot is unmanaged from PowerVC, the volume entry is removed from the PowerVC cinder database but they still remain in the storage backend. If the same virtual machine or volume is re-managed in PowerVC the consistency group and group snapshot information is lost.

Limitations

  • Consistency group is not supported for Shared Storage Pools, and GPFS.
  • Consistency group of in-use volumes is not supported in DS8K.
  • For PowerMax, consistency group for SRDF volumes is not supported.
  • Renaming of PowerMax groups is not allowed.
  • The following operations are not allowed if a volume is in a consistency group.
    • Volume Retype or Migration
    • Volume Delete
    • Clone Volumes
    • Virtual machine snapshot for the volumes in a consistency group.
    • Live Migration