Type of Dependency

The type of dependency defines the rigidity of the link between parent and child groups. There are three dependency types: soft, firm and hard.

Soft Dependency

In a soft dependency, VCS imposes minimal constraints while onlining parent/child groups. The only constraint is that child group must be online prior to the parent group being brought online; the location of the dependency determines where the child group must be online. For example, in an online local soft dependency, an instance of the child group must be online on the same system before the parent group can come online.

Soft dependency provides the following enhanced flexibility:

• If the child group faults, VCS does not immediately take the parent offline. If the child group cannot fail over, the parent remains online.
• When both groups are online, the child group can be taken offline while the parent is online and vice versa (the parent group can be taken offline while the child is online).
• To link a parent and child group, the child group is not required to be online if the parent is online. However, if the child group is also online, the parent and child may not be linked in such a way that their online states conflict with the type of link between parent and child.

The location of the link (local, global, or remote) designates whether or not a parent group will fail over after a fault and failover of the child group.

Firm Dependency

Firm dependency means VCS imposes more constraints when onlining parent/child groups. The child group must be online prior to the parent group being brought online; the location of the dependency determines where the child group must be online. In addition to the constraints imposed by soft dependency, firm dependency also includes the following constraints:

• If the child group faults, the parent is taken offline. If the child cannot fail over, the parent remains offline. However, if the child group faults and the parent group is frozen, the parent remains in its original state.
• The child group cannot be taken offline while the parent group is online. However, the parent group can be taken offline while the child is online.
• To link a parent and child group with firm dependency, the parent group must be offline or the parent and child group must be online in such a way that their online states do not conflict with the type of link between parent and child.

Both soft and firm dependencies allow that if the parent group faults, the child group does not. The parent group may or may not fail over, depending on the link constraints and locations (such as online local versus online global). See Service Group Dependency Configurations for more information.

Hard Dependency

A hard dependency imposes maximum constraints on linked service groups and provides a closer relationship between parent and child groups. In a hard dependency, the child and the parent groups fail over to the same system together when either the child or the parent faults.

The following restrictions apply when configuring a hard dependency:

• Only online local hard dependencies are supported.
• Only a single-level, parent-child relationship can be configured as a hard dependency.
• Bringing the child group online does not automatically bring the parent online.
• Taking the parent group offline does not automatically take the child offline.
• Bringing the parent online is prohibited if the child is offline.