Mount Failure - Transparent Failover Mode

Problem. EVM does not to correctly mount some BCV units when the storage is configured in transparent failover mode.

Cause. EVM cannot track target IDs. In transparent failover mode, two host ports on the controller pair are active. One controller port has a unit offset of 0 and the other port has an offset of 100. Consider the case of two units, D1 and D101, whose Access IDs allow them both to be seen by the same host. They may appear to the host operating system as:

Although the host operating system sees these as different units, EVM cannot distinguish between different target IDs and sees the two different units as the same device (LUN 1).

Solution: Distribute Units Across Adapters. When multiple adapters are available on a host, you can distribute the units appropriately across the adapters. This will divide the units across two separate SCSI ports and will eliminate the potential for mount problems. This method also has the benefit of balancing the I/O load across multiple adapters, thereby doubling bandwidth.

For example, if you have units D1 and D101, assign unit D1 to one adapter and unit D101 to another adapter.

Solution: Confine Visible Units to the Same Offset Range. You must keep all units that are visible to a single host within the same offset range, so they all appear under a single target ID. In transparent failover mode, this means confining each host's visible units to a single controller.

For example, assume that you have experienced mount problems on a storage subsystem with units D0-D2 and D100-D102 that are divided between Computer 1 and Computer 2. In reviewing Access IDs, you find that units D0, D1, D100 and D101 are assigned to Computer 1 and units D2, and D102 are assigned to Computer 2. These are LUN overlap conditions and EVM cannot distinguish between D0 and D100, or D1 and D101, on Computer 1; or between D2 and D102 on Computer 2.

To work correctly with EVM, you should assign units D0, D1 and D2  to Computer 1 and units D100, D101 and D102 to Computer 2. In this way, there will be no LUN overlap and EVM will see all three units on each host.