Storage Multi-Pathing choices in HP-UX Serviceguard environments, August 2009

Storage Vendor provided ‘plug-ins’ are needed to provide multi-pathing support of active/passive

arrays with Native Multi-Pathing on HP-UX 11i v3. Asymmetrical active/active arrays (active/active

arrays with a preferred controller) that are capable of Asymmetric Logical Unit Access (ALUA) do not

need a plug-in to work with Native Multi-Pathing as ALUA support has been implemented and

delivered in the HP-UX mass storage stack with 11i v3 Update 1 (fusion 0709). However prior to HP-

UX 11i v3 Update 1, the “preferred path” policy might work best for asymmetrical active/active

arrays like the HP StorageWorks EVA series. In a cluster, the administrator is responsible for

consistent configuration of the preferred path on all nodes.

With the introduction of Native Multi-Pathing in HP-UX 11i v3, which is bundled at no extra cost,

volume manager and arrays based solutions become less dominant or unneeded.

Native Multi-Pathing and LVM PVlinks (Alternate Links)

On HP-UX 11i v3, LVM relies on the Native Multi-Pathing functionality of the OS, which is

automatically enabled after an upgrade to HP-UX 11i v3 on existing volume groups with Legacy

DSFs. LVM supports use of both Legacy and Persistent DSFs on a system and even within an individual

volume group. This allows the transition to Persistent DSFs at the granularity of a pvol. Regardless of

which type of device file is being used, Native Multi-Pathing will be active by default. It is

recommended to convert existing Legacy DSFs to Persistent DSFs in existing environments to get

access to all the new features of the HP-UX 11i v3 mass storage subsystem. Further details about

Native Multi-Pathing with LVM and LVM migration from Legacy to Persistent DSFs can be found in:

LVM Migration from Legacy to Agile Naming Model.

Native Multi-Pathing and VxVM/CVM Dynamic Multi-pathing (DMP)

The details about DMP on HP-UX 11i v3 depend on the version of the volume manager in use and

whether it is VxVM or CVM.

At the time HP-UX 11i v3 released, Veritas Volume Manager (VxVM) 4.1 was the only supported

version of VxVM. With version 4.1, VxVM and Dynamic Multipathing (DMP) from Symantec are

supported on HP-UX 11i v3, but do not provide multi-pathing and load balancing. Veritas DMP acts

as a pass-through driver, allowing multi-pathing and load balancing to be controlled by the HP-UX

Native Multi-Pathing subsystem instead.

VxVM 4.1 does not support the agile view. Only Legacy DSFs are supported and subsequently, VxVM

configurations are subject to HP-UX 11i v2 limits. Further details are described in: Veritas 4.1 Installation

Guide (HP-UX 11i v3).

Symmantec VxVM and CVM 5.0 with DMP are now available on HP-UX 11i v3 and DMP provides

the following options:

 VxVM and CVM 5.0 support the Persistent DSFs.

 DMP on VxVM 5.0 volumes

– handles multi-pathing by default (enabled by Native Multi-Pathing functions)

– can be configured as pass-through or excluded (Native Multi-Pathing is performing multipathing

and load balancing)

 CVM 5.0 volumes require DMP to handle multi-pathing (enabled by Native Multi-Pathing functions)

HP StorageWorks SecurePath

HP StorageWorks SecurePath is no longer supported with HP-UX 11i v3 since the operating system

provides Native Multi-Pathing.

HP-UX 11i v3 supports the HP StorageWorks active/active disk arrays. The SecurePath virtual aliases

(/hpap/dsk/hpapX) for active/active disk arrays provided for the SecurePath managed LUNs are

not available after the OS upgrades to HP-UX 11i v3. Instead, use the new Persistent DSFs that are

introduced with HP-UX 11i v3 which provide the same function as the SecurePath virtual alias, are