HP Surestore Disk Array 12h - And FC60, Advanced User'S Manual, Page: 64 / 466

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Disk Array High Availability Features
Primary and Alternate I/O Paths
There are two I/O paths to each LUN on the disk array - one through controller A and one
through controller B. Logical Volume Manager (LVM) is used to establish the primary path
and the alternate path to a LUN. The primary path becomes the path for all host I/Os to that
LUN.
If a failure occurs in the primary path, LVM automatically switches to the alternate path to
access the LUN. The first time an I/O is performed to the LUN using the alternate path, the
disk array switches ownership of the LUN to the controller on the alternate path. Once the
problem with the primary path is corrected, ownership of the LUN should be switched
back to the original I/O path to maintain proper load balancing.
The primary path established using LVM defines the owning controller for the LUN. This
may override the controller ownership defined when the LUN was bound. For example, if
controller A was identified as the owning controller when the LUN was bound, and LVM
subsequently established the primary path to the LUN through controller B, controller B
becomes the owning controller.