Managing Serviceguard Sixteenth Edition, March 2009

To protect against Fibre Channel or SCSI bus failures, each copy of the data must be
accessed by a separate bus; that is, you cannot have all copies of the data on disk drives
connected to the same bus.
It is critical for high availability that you mirror both data and root disks. If you do not
mirror your data disks and there is a disk failure, you will not be able to run your
applications on any node in the cluster until the disk has been replaced and the data
reloaded. If the root disk fails, you will be able to run your applications on other nodes
in the cluster, since the data is shared. But system behavior at the time of a root disk
failure is unpredictable, and it is possible for an application to hang while the system
is still running, preventing it from being started on another node until the failing node
is halted. Mirroring the root disk allows the system to continue normal operation when
a root disk failure occurs.
Disk Arrays using RAID Levels and Multiple Data Paths
An alternate method of achieving protection for your data is to employ a disk array
with hardware RAID levels that provide data redundancy, such as RAID Level 1 or
RAID Level 5. The array provides data redundancy for the disks. This protection needs
to be combined with the use of redundant host bus interfaces (SCSI or Fibre Channel)
between each node and the array.
The use of redundant interfaces protects against single points of failure in the I/O
channel, and RAID 1 or 5 configuration provides redundancy for the storage media.
About Multipathing
Multipathing is automatically configured in HP-UX 11i v3 (this is often called native
multipathing), or in some cases can be configured with third-party software such as
EMC Powerpath.
NOTE: 4.1 and later versions of Veritas Volume Manager (VxVM) and Dynamic
Multipathing (DMP) from Symantec are supported on HP-UX 11i v3, but do not provide
multipathing and load balancing; DMP acts as a pass-through driver, allowing
multipathing and load balancing to be controlled by the HP-UX I/O subsystem instead.
For more information about multipathing in HP-UX 11i v3, see the white paper HP-UX
11i v3 Native Multipathing for Mass Storage, and the Logical Volume Management volume
of the HP-UX System Administrator’s Guide in the HP-UX 11i v3 Operating
Environments collection at http://docs.hp.com. See also “About Device File
Names (Device Special Files)” (page 107).
Monitoring LVM Disks Through Event Monitoring Service
If you are using LVM, you can configure disk monitoring to detect a failed mechanism
by using the disk monitor capabilities of the EMS HA Monitors, available as a separate
product (B5736DA). Monitoring can be set up to trigger a package failover or to report
Redundant Disk Storage 45