Overview: The Next Generation Mass Storage Stack (September 2009)

For information on the interaction between native multi-pathing and third-party multi-pathing products such as
SecurePath and VERITAS DMP, see the impacts section on Third-Party Multi-Pathing Products
.
If you are using LVM alternate links to manage multi-pathed LVM disks, see the impacts section on Logical Volume
Manager.
Command changes include the following:
ioscan –m lun
Displays the multiple paths to a LUN.
ioscan –P health
Indicates whether a lunpath is disabled.
scsimgr
Enables the selection of different load balancing algorithms, either for a single LUN, a set of
LUNs, or all LUNs, by setting the load_bal_policy attribute. Also controls whether
legacy DSFs allow multi-pathing, by setting the leg_mpath_enable attribute.
For additional information on multi-pathing and agile addressing in HP-UX 11i v3, see the HP-UX 11i v3 Native
Multi-Pathing for Mass Storage white paper in For more
information.
Adaptability
The next generation mass storage stack enhances the ability of a server to adapt dynamically to hardware
changes, without shutting down the server or reconfiguring software.
Background
Asynchronous changes to a server usually require some action on your part; for example, adding a new disk
requires the creation of new DSFs. Over the last several releases, HP-UX has been enhanced to automatically
adapt to a changing environment, and HP-UX 11i v3 continues this trend.
A server running HP-UX 11i v3 automatically detects the creation or modification of SCSI LUNs. If new LUNs are
added, persistent DSFs are automatically created. If the addressing, size, or I/O block size of an existing LUN
changes, the mass storage stack detects this without user intervention.
When such changes occur, the mass storage stack notifies any relevant subsystems. For example, if a LUN
expands (dynamic LUN expansion), its associated disk driver, volume manager, and file system are notified.
The volume manager or file system can then automatically expand a volume group and file system.
The next generation mass storage stack can also remove PCI host bus adapters (HBAs) without shutting down the
server. Coupled with existing online addition and replacement features, online deletion enables you to replace a
PCI card with a different PCI card, as long as the HBA slot permits it and no system critical devices are affected.
You can also change the driver associated with a LUN; if the software drivers do not support rebinding online, the
system remembers the changes and defers them until the next server reboot.
The I/O subsystem now maintains dynamic status for mass storage and networking devices. Each device and HBA
now has a health property that you can print with the ioscan command. The boot and crashdump subsystems
monitor the status of multi-pathed devices, and automatically failover to an alternate available path if an existing
path goes offline.
You can also track down stale devices, that is, devices that are configured on a server but no longer physically
connected, and remove their definitions from the system.
Impact
Command changes include the following:
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