Installation and Reference Guide HP StorageWorks Secure Path 3.0F Service Pack 4 for HP-UX 11i v1.0 and 11i v2.0 (5697-8001, March 2009)

When a failure occurs, Secure Path marks the affected path as failed. This removes it from the list
of usable paths for the LUN. If no active paths remain on the same controller, Secure Path attempts
to move the device to a standby controller.
Failback options
Secure Path lets you set the path failback option to manual mode or automatic mode.
• In manual mode, you must enter a management utility command to restore devices to their preferred
path. The operation is performed even if system I/O is in process to the selected device.
• In automatic mode, Secure Path tests a failed path at fixed intervals if I/O is in process for the
affected device. If the path appears to be viable, the path state is set to active and I/O is routed
through this path.
Load balancing
When enabled without selecting a policy, load balancing allows multiple paths between a host and
a specific LUN to be used in a round-robin fashion. Using multiple paths spreads the load across all
components in the RAID storage system and maximizes performance.
Load balancing may not be used in environments that have device reservations as a lock mechanism
because the RAID array controllers enforce reservations on a per-port basis.
Load balancing requires a Fibre Channel configuration that results in at least four unique paths from
the host node to the storage system. While this can be accomplished with several different physical
configurations, maximum performance potential is achieved when all four ports of the RAID storage
systems are used.
When load balancing is enabled, the Secure Path driver by default, marks all the owning controller
as active. This is true when the following conditions occur:
• A host boots up.
• Secure Path fails over a LUN from one controller to the other.
• You manually move a selected LUN between controllers using the Secure Path Manager utility,
spmgr.
Secure Path supports four types of load balancing policies:
• Round Robin — I/O is routed through the paths of the active controller in a round-robin fashion.
• Least I/O — I/O is routed through the path that has the least amount of I/O requests.
• Least Service Time — I/O is routed through the path that has the least completion time for an I/O
request.
• Least Bandwidth — I/O is routed through the path that has the least amount of bytes queued.
Path verification
When enabled with spmgr, path verification causes Secure Path to periodically test the availability
of all paths to all LUNs for paths marked available, failed, active, or standby. Path verification does
not test paths that are in a quiesced state.
Path verification is useful for detecting failures that affect overall path redundancy before they affect
failover capability. If an active path fails path verification, failover occurs. If an available path fails
path verification, its state changes from available to failed.
If a path marked failed passes path verification, the path state is set to available, and if auto-restore
is enabled, the path becomes active. If the path is on the active controller, it is marked preferred.
Secure Path for Active-Passive disk arrays18