FC target assigned to pool properties
This function allows modifying target alias and assign a remote target. Configuration of the remote target is crucial for a correct FC cluster configuration. FC targets are local to a particular machine because in general those are the physical ports from adapters attached to a given server. In cluster environment when a pool has to be moved to other node, it is required to know which target should be used there to serve FC groups resources. In order to properly configure FC for a cluster use, it is required to assign a remote target to each of local targets present in FC groups.
Cluster uses Asymmetric Logical Unit Access (ALUA) to configure the paired targets. LUNs are visible on both configured targets by the initiator that has access to those LUNs by paths. Depending on the path status, the initiator knowns which path should be used to access LUNs. Initiator accesses LUNs by using an active path and standby path is used for a target that doesn’t have access to LUNs. Active path is set for a target, when the pool is present on the same node where the target is. Standby path is used for a target, when a pool is present on the other node. When a cluster moves the pool from one node to another, path statuses are modified accordingly. If the remote target is not configured, ALUA configuration is not created by cluster on the remote node. In that case, after moving the pool, all resources served by that target won’t be accessible. Once the remote target is assigned, the cluster performs configuration of ALUA and a given target can be safely used by both cluster nodes. It is possible to assign the remote target before or after cluster start, but it is necessary to make sure that it is configured before the move of pool is performed (either manually or by failover). Moreover, after assignment of remote target please make sure that it is in the target mode on the remote node. If the remote target will be in an initiator mode, it won’t be possible to access target LUNs after a pool move, despite modification of path statuses.
In summary, to correctly set up targets for cluster use it is required to:
- Select a remote target for each target assigned to FC groups.
- Switch a selected remote target on remote node to target mode.