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What Happens to a Shadow Set When a System Fails?   



When a system, controller, or disk failure occurs, the shadowing software maintains data availability by performing the appropriate copy, merge, or minimerge operation. The following subsections describe the courses of action taken when failures occur. The course of action taken depends on the event and whether the shadow set is in a steady state or a transient state.

Transitions from Steady State

When a shadow set is in a steady state, the following transitions can occur:

Once the transition completes, the disks contain identical information and the shadow set returns to a steady state.

Transitions During Copy and Minicopy Operations

The following list describes the transitions that can occur to a shadow set that is undergoing a copy or minicopy operation. The transitions apply to both forms of copy operations except where noted:

When a node failure occurs during a shadow set copy operation, merge behavior depends on whether or not the shadowing performance assists are enabled.

Transitions During Minimerge Operations

When a shadow set is undergoing a minimerge operation, the following transitions can occur:

Transitions During Merge Operations

The following list describes the transitions that can occur to the shadow set that is undergoing a merge operation when performance assists are not available:


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