Rules for SSA Loops

Rules for SSA Loops

For SSA loops that include the SSA RAID Cluster Adapter, the following rules apply:

Example of a Clustered Configuration

The following diagram shows two SSA RAID Cluster Adapters in two loops:


Clustering Implementation

Two SSA RAID Cluster Adapters can be connected in one or two SSA loops with SSA disk drives. In this arrangement, the adapter with the higher SSA Unique ID is considered the primary  adapter for all the arrays that are configured on the adapters. Commands for an array from the adapter that is not the primary adapter are automatically routed to the primary adapter to be implemented. Such an arrangement is called a Cluster 

All the arrays are reported to both systems. The system software determines which server to use to communicate to each array.

If the non-primary adapter detects that it has lost access to the other adapter across the SSA loop, the non-primary adapter becomes the primary adapter. Commands sent to the old primary adapter are resent to the new primary adapter. This is failover .
Each adapter checks periodically that it can still communicate with its host. If it fails, it stops operating, this is detected by the other adapter and the network is reconfigured.

If write operations are in progress to an array (or have been received within the previous 20 seconds) when failover occurs, the array is rebuilt after the new primary adapter has taken control.

If an array has one of its members missing (that is, the array is in the exposed or degraded state) when a failover occurs, the status of the array becomes offline and an error is logged. Manual intervention is needed to resolve this error.

After a failover has occurred and a new adapter has been installed in place of the faulty one, the new adapter might have an SSA Unique ID that is higher than that of the remaining (currently primary) adapter. If this is the case, the new adapter becomes the primary adapter. This is failback .

The maximum configurations are:

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