1.2.20.6 Volume Groups

A volume group is a specific collection of Exascale volumes.

Volume groups can be used to:

• Easily identify volumes with a common purpose or inherent relationship.

  For example, you can use a volume group to collect all the volumes underpinning the image files associated with an individual virtual machine (VM). Also, you can optionally name the volume group, making it easier to understand its purpose and distinguish it from numerous other groups.

• Collectively manage I/O resources consumed by all volumes in the group.

  A volume group can optionally be configured as a resource-sharing volume group, using either aggregate or specified resource sharing.

  Under aggregate resource sharing, the volume group automatically shares the total I/Os per second (IOPS) bandwidth provisioned to all volumes in the group. In this case, an individual volume can exceed its volume-level limit by sharing unused IOPS provisioned to other volumes in the group. But the entire group is always governed by the aggregated limit.

  With specified resource sharing, a specific IOPS bandwidth limit is associated with the volume group. In this case, the group is governed only by the specified limit.

  In either case, a resource-sharing volume group also works in conjunction with I/O resource management (IORM) directives defined at other levels, such as the Exascale vault level.

• Efficiently create consistent snapshots of all volumes in a volume group.

  In one operation, you can create a set of volume snapshots with point-in-time consistency, which are easily identifiable by a unique batch ID.

Note the following details about volume groups:

• A volume group can contain only writable volumes, including volume clones. Volume snapshots cannot be part of a volume group.

• All volumes belonging to a volume group must reside in the same Exascale vault.

• A volume must always have at least one owner in common with each volume group it belongs to.

• A volume can be a member of up to five different volume groups. However, at any time, a volume can belong to only one resource-sharing volume group.