Managing Serviceguard Fifteenth Edition, reprinted May 2008

Understanding Serviceguard Hardware Configurations
Redundant Disk Storage
Chapter 246
When planning and assigning SCSI bus priority, remember that one
node can dominate a bus shared by multiple nodes, depending on what
SCSI addresses are assigned to the controller for each node on the
shared bus. All SCSI addresses, including the addresses of all interface
cards, must be unique for all devices on a shared bus.
Data Protection
It is required that you provide data protection for your highly available
system, using one of two methods:
• Disk Mirroring
• Disk Arrays using RAID Levels and Multiple Data Paths
Disk Mirroring
Serviceguard itself does not provide protection for data on your disks, but
protection is provided by HP’s Mirrordisk/UX product for LVM storage,
and by the Veritas Volume Manager for VxVM and CVM.
The logical volumes used for Serviceguard packages should be mirrored;
so should the cluster nodes’ root disks.
When you configure logical volumes using software mirroring, the
members of each mirrored set contain exactly the same data. If one disk
fails, the storage manager automatically keeps the data available by
using the mirror. you can use three-way mirroring in LVM (or additional
plexes with VxVM) to allow for online backups or to provide an
additional level of high availability.
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