HP 6400/8400 HP StorageWorks 6400/8400 Enterprise Virtual Array User Guide - Page 39

1 If preference has been configured to ensure a more balanced controller configuration, the Path A/B - Failover/Failback setting is required to maintain the configuration after a single controller reboot. Changing virtual disk failover/failback setting Changing the failover/failback setting of a virtual disk may impact which controller presents the disk. Table 13 (page 39) identifies the presentation behavior that results when the failover/failback setting for a virtual disk is changed. NOTE: If the new setting causes the presentation of the virtual disk to move to a new controller, any snapshots or snapclones associated with the virtual disk will also be moved. Table 13 Impact on virtual disk presentation when changing failover/failback setting New setting No Preference Path A Failover Path B Failover Path A Failover/Failback Path B Failover/Failback Impact on virtual disk presentation None. The disk maintains its original presentation. If the disk is currently presented on controller B, it is moved to controller A. If the disk is on controller A, it remains there. If the disk is currently presented on controller A, it is moved to controller B. If the disk is on controller B, it remains there. If the disk is currently presented on controller B, it is moved to controller A. If the disk is on controller A, it remains there. If the disk is currently presented on controller A, it is moved to controller B. If the disk is on controller B, it remains there. Implicit LUN transition Implicit LUN transition automatically transfers management of a virtual disk to the array controller that receives the most read requests for that virtual disk. This improves performance by reducing the overhead incurred when servicing read I/Os on the non-managing controller. Implicit LUN transition is enabled in VCS 4.x and all versions of XCS. When creating a virtual disk, one controller is selected to manage the virtual disk. Only this managing controller can issue I/Os to a virtual disk in response to a host read or write request. If a read I/O request arrives on the non-managing controller, the read request must be transferred to the managing controller for servicing. The managing controller issues the I/O request, caches the read data, and mirrors that data to the cache on the non-managing controller, which then transfers the read data to the host. Because this type of transaction, called a proxy read, requires additional overhead, it provides less than optimal performance. (There is little impact on a write request because all writes are mirrored in both controllers' caches for fault protection.) With implicit LUN transition, when the array detects that a majority of read requests for a virtual disk are proxy reads, the array transitions management of the virtual disk to the non-managing controller. This improves performance because the controller receiving most of the read requests becomes the managing controller, reducing proxy read overhead for subsequent I/Os. Implicit LUN transition is disabled for all members of an HP P6000 Continuous Access DR group. Because HP P6000 Continuous Access requires that all members of a DR group be managed by the same controller, it would be necessary to move all members of the DR group if excessive proxy reads were detected on any virtual disk in the group. This would impact performance and create a proxy read situation for the other virtual disks in the DR group. Not implementing implicit LUN transition on a DR group may cause a virtual disk in the DR group to have excessive proxy reads. Storage system shutdown and startup The storage system is shut down using HP P6000 Command View. The shutdown process performs the following functions in the indicated order: Storage system shutdown and startup 39