LVM Migration from Legacy to Agile Naming Model

Storage. This is the default behavior in the case of active/active devices, irrespective of the naming model used.
Some active/passive devices may be supported by the mass storage stack but will be managed by the respective
vendor delivered plug-in modules. For additional information on writing active/passive device plug-ins in HP-UX
11i v3, see the
For More Information section for the white paper HP-UX 11i v3 Writing Active/Passive Switch
Plug-Ins.
Due to the native multi-pathing functionality of the mass storage stack, the behavior of LVM alternate link and LVM
online disk replacement functionalities may differ when compared with previous releases.
LVM Alternate Links (PVlinks)
LVM supports alternate links to a device to allow continued access to the device if the primary link fails. In
previous HP-UX releases, (that is, HP-UX 11i v2 or earlier) LVM’s multi-pathing solution increases the data
availability but does not allow multiple paths to be used simultaneously. LVM continues to support this
functionality even in HP-UX 11i v3, but the behavior may be very different based on how LVM and the mass
storage stacks are configured.
With the introduction of mass storage stack’s native multi-pathing functionality, it is no longer required nor
recommended to configure LVM alternate links.
Listed below are the alternate link behavioral differences that could be seen, when compared with previous
releases:
• Regardless of whether LVM alternate links are configured or not, the mass storage stack processes the I/O
operations to the device using all available paths. That is, LVM selects the LUN and the mass storage stack
selects the lunpath to be used.
• If LVM alternate links are configured, no link switching ever happens unless the mass storage stack’s native
multi-pathing feature is disabled using the scsimgr command and only legacy DSFs are used in the volume
group configuration. For additional information on scsimgr command capabilities in HP-UX 11i v3, see the
For More Information section for the white paper scsimgr SCSI Management and Diagnostics Utility on HP-UX
11i v3.
• Path switch options of the pvchange (-s and –S options) command do not switch links or stop I/O operations,
as they did in earlier releases. In order to disable I/O operations on a given path, use the scsimgr command
(scsimgr [-f] disable Lunpath).
• While LVM alternate link functionality supports up to 8 paths to a physical volume, mass storage stack’s native
multi-pathing feature can support up to 32 lunpaths.
Restoring LVM’s Legacy Alternate Link Behavior
If legacy LVM alternate link functionality is preferred over the mass storage stack’s native multi-path functionality,
the native multi-pathing feature can be disabled using scsimgr command. This can be accomplished by setting the
device attribute leg_mpath_enable to false. This attribute is available on both global (system wide) and on a per-
LUN basis. The value of per-LUN tunable overrides the global value. As this feature is available only on legacy
DSFs, LVM volume groups must be configured using legacy DSFs.
Note: Multi-pathing is not affected by this attribute when persistent DSFs are used.
The following example shows how to enable legacy LVM alternate link functionality in a backward compatible
manner. In this example, the volume group vg01 is configured with a single persistent DSF.
1. Get a list of DSFs configured in the volume group:
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