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

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In addition to path failover and load balancing, SecurePath also monitors the path’s health to allow

automatic fail-back after a path is repaired and to proactively identify issues with idle paths. For more

information about HP StorageWorks SecurePath please see the “HP StorageWorks SecurePath 3.0F

Service Pack 2 for HP-UX 11i v1.0 and 11i v2.0, installation and reference guide”.

EMC PowerPath

EMC PowerPath is also a purchasable software product that provides path management. Individual

features are automatic path failover in the event of a hardware failure, dynamic load balancing

between the paths, proactive I/O path testing and automatic path recovery upon restoration of a

failed path. PowerPath offers various failover and load balancing policies.

Besides Symmetrix and CLARiiON storage systems PowerPath also extended support to a range of HP

StorageWorks arrays including the XP and EVA systems. While PowerPath is optional for most

storage systems in a Serviceguard cluster, for CLARiiON storage systems the use of PowerPath is

mandatory in a Serviceguard cluster if the nodes are on HP-UX 11i v2.

Further information about PowerPath can be found in the product specific documentation like

“PowerPath for HP-UX Version 4.5 Installation and Administration Guide (P/N 300-002-383, Rev

A03) “ and “PowerPath Version 4.5 Product Guide (P/N 300-002-834 REV A03) “

Multi-pathing solutions for HP Virtual Machine

All multi-pathing solutions discussed above are supported with the current version – A.04.00 – of HP

Virtual Machines (HPVM) with the multi-pathing software running on the HPVM host. Currently multi-

pathing solutions must be implemented on the HPVM host and not the guest.

Selection and coexistence of different multi-pathing solutions

In general, customers can choose among the multi-pathing solutions available on HP-UX 11i v2. The

selection of a storage system and a volume manager used in a Serviceguard cluster reduces the

number of available multi-pathing solution in a specific configuration. For example a cluster which

uses LVM as a volume manager and an EMC Symmetrix as shared storage, can’t deploy DMP or

SecurePath as multi-pathing solution. Customers which implement one of the Serviceguard Storage

Management Suite bundles most likely will choose DMP since it is included in all of those bundles. If

multiple solutions are feasible, the following criteria are often used to select a multi-pathing solution:

 Cost: Does the multi-pathing software incur additional cost? PVlinks and DMP either come with the

HP-UX or Serviceguard SMS. SecurePath and EMC PowerPath need to be purchased additionally.

 Multi-platform support: Often customers standardize on certain technologies. This might be the host

operating system, the volume manager, or the storage array and they prefer to use the same multi-

pathing solution throughout their computing environment. If this criteria has the highest priority for a

customer, their standardization strategy predetermines the multi-pathing solution. Customers

standardizing on VxVM/CVM volume manager might prefer DMP; others that standardize on EMC

storage systems might prefer PowerPath.

 Dynamic load balancing: If dynamic load balancing is of great importance, a customer might

rather invest in a storage platform specific multi-pathing solution or DMP than implementing LVM

PVlinks.

Typically only one multi-pathing solution is installed on a system. In rare situations several multi-

pathing solutions could be present on a system. However it does not add an extra level of high