Changing Virtual Disk Failover/Failback Setting; Implicit Lun Transition; Impact On Virtual Disk Presentation When Changing Failover/Failback Setting - HP StorageWorks 4400 User Manual

Setting

Changing virtual disk failover/failback setting

Changing the failover/failback setting of a virtual disk may impact which controller presents the disk.
Table 11 identifies the presentation behavior that results when the failover/failback setting for a virtual
disk is changed.
NOTE:
If the new setting moves the presentation of the virtual disk to a new controller, any snapshots or
snapclones associated with the virtual disk are also moved.
Table 11 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

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.
Point in time
On dual boot or controller resynch
On controller failover
On controller failback
Impact on virtual disk presentation
None. The disk maintains its original presentation.
If the disk is currently presented on Controller 2, it is moved to
Controller 1. If the disk is on Controller 1, it remains there.
If the disk is currently presented on Controller 1, it is moved to
Controller 2. If the disk is on Controller 2, it remains there.
If the disk is currently presented on Controller 2, it is moved to
Controller 1. If the disk is on Controller 1, it remains there.
If the disk is currently presented on Controller 1, it is moved to
Controller 2. If the disk is on Controller 2, it remains there.
HP StorageWorks 4400 Enterprise Virtual Array user guide
Behavior
If cache data for a LUN exists on a partic-
ular controller, the unit will be brought
online there. Otherwise, the units are
brought online to Controller 2.
All LUNs are brought online to the surviv-
ing controller.
All LUNs remain on the surviving control-
ler. After controller restoration, the units
that are online to Controller 1 and set to
Path B are brought online to Controller 2.
This is a one-time occurrence. If the host
then moves the LUN using SCSI com-
mands, the LUN will remain where moved.
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