User guide

Technical white paper | HP Enterprise Virtual Array Storage and VMware vSphere 4.x and 5.x configuration best practices
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Vdisk provisioning
All EVA active-active arrays are asymmetrical and comply with the SCSI ALUA standard.
When creating a Vdisk on an EVA array, you have the following options for specifying the preference for the managing
controller for that Vdisk:
• No Preference
– Controller ownership is non-deterministic; Vdisk ownership alternates between controllers during initial presentation
or when controllers are restarted.
– On controller failover (owning controller fails), Vdisks are owned by the surviving controller.
– On controller failback (previous owning controller returns), Vdisks remain on the surviving controller; no failback occurs
unless explicitly triggered.
• Path A-Failover only
– At presentation, the Vdisk is owned by Controller A.
– On controller failover, the Vdisk is owned by Controller B.
– On controller failback, the Vdisk remains on Controller B; no failback occurs unless explicitly triggered.
• Path A-Failover/failback
– At presentation, the Vdisk is owned by Controller A.
– On controller failover, the Vdisk is owned by Controller B.
– On controller failback, the Vdisk is owned by Controller A.
• Path B-Failover only
– At presentation, the Vdisk is owned by Controller B.
– On controller failover, the Vdisk is owned by Controller A.
– On controller failback, the Vdisk is owned by Controller A; no failback occurs unless explicitly triggered.
• Path B-Failover/failback
– At presentation, the Vdisk is owned by Controller B.
– On controller failover, the Vdisk is owned by Controller A.
– On controller failback, the Vdisk is owned by Controller B.
In the event of a controller failure that triggers the failover of all owned Vdisks to the alternate controller, it is critical that,
when the failed controller is restored, Vdisk ownerships that were failed over to the surviving controller are failed back to
the restored controller. This action ensures that, after a controller failover, the system can return to its default
balanced/configured state and that all Vdisks do not end up on a single controller, degrading system performance.
With vSphere 4.x and 5.x and earlier versions of ESX, it is highly recommended to use one of the following preferences when
configuring EVA Vdisks:
• Path A-Failover/failback
• Path B-Failover/failback
These preferences ensure that Vdisk ownership is restored to the appropriate controller when a failed controller is restored.
Vdisks should be created with their controller failover/failback preference alternating between Controller A and B.
The above recommendations provide additional benefits in a multi-pathing configuration, as described in Configuring multi-
pathing.
Best practice controller ownership
• Controller ownership for EVA Vdisks should alternate between Controller A and Controller B, using the Path-A-
Failover/Failback or Path-B-Failover/Failback setting.