HP-UX 11i v3 Native Multi-Pathing for Mass Storage (August 2012)

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Overview
Features
Multi-pathing is the ability to manage the various paths to a LUN device. A path to a LUN is also
known as an I_T_L nexus. It corresponds to the route taken by an I/O request issued from an HP-UX
host to a SCSI device.
The following is an overview of the native multi-pathing features. For more information, see
Native
Multi-Pathing Features.
• LUN WWID and DSF — The various paths to LUN devices are correlated based on a world-wide
unique identifier (WWID) that is used to create a persistent DSF offering agile addressing.
• Dynamic I/O load-distribution — The I/O load to a LUN is optimally and transparently distributed
across the available lunpaths.
• High availability of SCSI devices — To optimize access to LUNs, the mass storage stack
transparently performs lunpaths error detection, recovery, and automated failover.
• LUN failure management — When LUN failure conditions occur, the mass storage stack
automatically recovers whenever possible. If necessary, administrators can use the new
scsimgr
command to recover from the LUN failure.
• Active-Passive device support
• SAN dynamic discovery and reconfiguration — Proactive and automatic discovery of new paths
allow application I/O traffic to be dynamically balanced across the most up-to-date set of active
lunpaths. New DSFs are automatically created for newly discovered LUN devices. The health of
LUNs and lunpaths is also dynamically updated as LUNs and lunpaths availability changes. The
LUNs and lunpaths health is also made available to user applications through tools like
ioscan.
• Full integration with HP-UX 11i v3 — Existing tools (for instance ioscan, sar, and smh) and HP-
UX subsystems (for instance boot, dump, file systems (HFS), the Logical Volume Manager (LVM))
have been enhanced to use native multi-pathing. In addition, new tools like scsimgr are provided
to manage the native multi-pathing solution.
• Compatibility with the legacy naming model — Legacy lunpath DSFs are available on HP-UX 11i
v3 for backward compatibility reasons. High availability is ensured by default on legacy DSFs
through native multi-pathing. A tunable is provided to enable and disable native multi-pathing on
legacy DSF.
• Pre-HP-UX 11i v3 multi-pathing add-on products are no longer required.
Benefits
The benefits of native multi-pathing are as follows:
Optimal use of system resources
The mass storage subsystem optimally uses system resources such as memory and processors to
perform I/O operations as efficiently as possible. For instance, on systems supporting cell local
memory, you can tune the I/O load distribution to reduce memory, interrupt and device latencies
using the cell local round robin I/O load balancing policy. For more information, see
Disk LUN load
balancing selection.
Optimal use of SAN resources
The I/O path selection is optimized to achieve best I/O data throughput. For each SCSI device class,
the mass storage subsystem offers multiple I/O load balancing policies. You can select a load
balancing policy and tune it to take into account the idiosyncrasies of the SAN configuration.