FC target assigned to pool properties
The article describes how to assign FC target to pool properties when using HA cluster or single node configuration. In general, this function allows modifying target alias and assigning a remote target. In addition, if you would like to learn about FC target replacement, read this article: http://wiki.open-e.com/default/wiki/FC_target_replacement
High Availability cluster configuration
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 a cluster environment, when a pool has to be moved to other node, it is is required to know which target should be used there to serve FC groups resources. 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.
The 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. The initiator accesses LUNs by using an active path and a standby path is used for a target that doesn’t have access to LUNs. The active path is set for a target, when the pool is present on the same node where the target is. The 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, the ALUA configuration is not created by a 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 the 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 the cluster is started, 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 the assignment of a 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 the modification of path statuses.
In summary, to correctly set up targets for a cluster usage, do the following:
- Select a remote target for each target assigned to FC groups.
- Switch a selected remote target on a remote node to a target mode.
Single node configuration
There is no possibility to pair the target with a remote node because ALUA is not used. In case when the pool is imported with an FC configuration from another machine, it is neccessary to assign FC targets to FC ports of the current server. This is due to the fact that the system is unable to determine on which ports it has to share resources.