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

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New SAN resources are readily made available to the host because of the automated discovery of
SCSI devices. You can delete stale SAN resources to free up system resources.
Scalability
The mass storage subsystem can theoretically address up to 2
24
(16 million) LUNs. There is no
architectural limit on the number of lunpaths allowed to a LUN. For information on the maximum
number of LUNs and lunpaths that were tested, see the HP-UX 11i v3 Release Notes.
However, the mass storage subsystem has not removed any scalability limitations present in previous
releases of HP-UX for legacy DSFs.
Built-in high availability of SAN resources
The mass storage subsystem quickly identifies failing SAN components and takes action to recover
from the error to minimize the impact on applications using the SAN resources. The mass storage
subsystem proactively monitors and reports lunpath error conditions and provides error recovery
mechanisms. When a lunpath fails, the mass storage subsystem switches the I/O flow to other
available lunpaths (path failover) while recovery is attempted on the failing lunpath. Depending
upon the circumstances, a failing lunpath component can either automatically recover (self-
healing), or the mass storage subsystem notifies the system administrator who can take appropriate
action.
Increased I/O performance
The optimal use of system and SAN resources in the selection of lunpaths leads to significant
improvements in I/O throughput. For more information, see the
HP-UX 11i v3 Mass Storage I/O
Performance Improvements white paper.
Ease of management
Native multi-pathing is easy to manage for the following reasons:
• The agility of LUN addressing achieved through the use of LUN WWID makes LUN DSFs immune to
certain SAN topology changes, such as for instance the addition of new lunpaths to a LUN device.
• Existing HP-UX commands such as ioscan, sar, insf, and rmsf have been enhanced to handle
LUN multi-pathing. For instance, ioscan has a new
–m option (map option) to display the mapping
between lunpath hardware paths and LUN hardware paths. The sar command has a new –L
option to display data throughput of lunpaths.
• New tools have been introduced. The new command line utility scsimgr manages the mass
storage subsystem. It is integrated with HP System Management Homepage to offer a graphical
user interface. See the
scsimgr SCSI Management and Diagnostics Utility white paper.
• System administrators no longer have to learn commands specific to multi-pathing add-on products.
• The mass storage subsystem performs quick components fault notification via statistics, diagnostics
messages, and tunables.
• Tools such as ioscan and scsimgr, and mechanisms internal to the mass storage subsystem,
give an up-to-date view of the SAN components connected to the host at any time. As the SAN
topology evolves, the host system view of the SAN is updated. The ioscan and scsimgr
commands also provide easy ways to display the relationships between SAN components.
• Dynamic discovery of SCSI devices automatically provides system administrators with the most up-
to-date view of SAN resources.