Veritas 4.1 Installation Guide (HP-UX 11i v3, February 2007)

8 VxVM 4.1, New Style DSFs and HP-UX Native
Multipathing
Introduction
HP-UX 11i v3 introduces a new representation for the mass storage devices called the agile view.
The central idea behind the agile view is that the disk devices and tape drives are identified by
the actual object, and not by a hardware path to the object.
Legacy View (Old Style DSFs)
Prior to HP-UX 11iv3, DSFs for mass storage devices had their hardware path, or lunpath, encoded
in their name and their minor number. For example, the DSF /dev/dsk/c3t15d0 is at SCSI
controller instance 2, SCSI target 15, and SCSI LUN 0.
Agile View (New Style DSFs)
On HP-UX 11iv3, you can create persistent DSFs. Persistent DSFs allow you to create a single
DSF for each unique LUN on the server, no matter how many lunpaths the LUN has or how
many of those lunpaths have changed. With persistent binding, the DSF name and minor number
no longer have hardware path information encoded in them. Instead, they have a simple device
instance number such as /dev/disk/disk3. Rather than mapping to the LUN hardware path,
the persistent DSFs map to the LUN World Wide Identifier (WWID), a resource on the LUN
similar to a serial number. The WWID is unique to a LUN and does not change for that LUN. If
any of lunpaths change for a LUN, the DSF bound to the LUN does not need to change.
VxVM does not support New Style DSFs.
WARNING! DO NOT disable the legacy DSFs using any of the commands like rmsf –L as
VxVM 4.1 on HP-UX 11i v3 does not support the new style DSFs. If the system is VxVM rooted,
it will not be bootable if legacy DSFs are disabled. VxVM volumes created on HP-UX 11i v2,
cannot be accessed on HP-UX 11i v3 systems if you accidentally disable the legacy DSFs after
you do an update-ux.
HP-UX Native Multipathing and Veritas DMP
The HP-UX 11i v3 I/O subsystem provides multipathing and load balancing by default.
Veritas Volume Manager (VxVM) 4.1 and Dynamic Multipathing (DMP) from Symantec are
supported on HP-UX 11i v3, but do not provide multipathing and load balancing; Veritas DMP
acts as a pass-through driver, allowing multipathing and load balancing to be controlled by the
HP-UX I/O subsystem instead.
When you upgrade to a system to HP-UX 11i v3, the I/O subsystem will start performing load
balancing and multipathing for all multipath devices (whether or not they are managed by
VxVM/DMP); you do not have to take any additional steps to make this happen.
For more information about multipathing in HP-UX 11i v3, see the white paper “HP-UX 11i v3
Native Multipathing for Mass Storage” on http://docs.hp.com.
Veritas DMP Behavior on HP–UX 11iv3
• Veritas DMP is in pass-through mode and hence does not perform failover when a path to
a LUN fails and continues to show the state of the path as active until HP-UX native
multipathing fails an I/O or ioctl request on that path.
• The default I/O policy for Veritas DMP is set to single active for all types of enclosure. When
Veritas DMP receives or sends I/O on a legacy path, native multipathing chooses the
Introduction 69