HP-UX System Administrator's Guide: Routine Management Tasks

Using High Available Storage Systems (HASS)
High Available Storage Systems (HASS) provide two internal SCSI busses, each with
their own connectors, power cords, power supplies, and fans. This hardware
redundancy, when combined with software ing, can prevent most single point of failure
problems. HASS do not provide any RAID support on their own.
Pros and Cons of HASS
There are many advantages of systems protected by HASS. These include disk storage
modules that are hot-pluggable which means that the bus and connectors are made
so that the disk module can be inserted or removed without removing the terminator
for the array. All hardware modules are easily removed from the front of the chassis.
HASS do not have the problems of previous disk configurations that required extra-long
F/W SCSI cables, the removal of the chassis from the cabinet, and the removal of the
cover before individual disk mechanisms can be replaced.
The negative side of HASS is that operating system cooperation is still required when
removing a disk module from the HASS since the HASS does not provide any data
protection or regeneration of data on a newly replaced disk module. HASS is primarily
a hardware protection strategy and software mirroring is required to implement a
mirroring scheme on HASS.
Recommended Uses of HASS
The HASS protection system is an excellent step in preventing single points of failure
and is recommended for systems that must be available as much of the time as possible.
Serviceguard can employ HASS for additional data storage. See“Using Serviceguard”
(page 210).
Using Serviceguard
An Serviceguard cluster is a networked grouping of HP 9000 servers (nodes) having
sufficient redundancy of software and hardware that a single point of failure will not
significantly disrupt service. Applications and services are grouped together in packages.
In the event of a service, node, or network failure, Serviceguard can automatically
transfer control of all system resources in a designated package to another node within
the cluster, allowing the applications to remain available with minimal system
interruption.
Serviceguard replaces the earlier SwitchOver product which also allowed for redundant
computer systems. Serviceguard first became available with HP-UX 10.0.
Pros and Cons of Serviceguard
To provide a high level of availability, a typical cluster uses redundant system
components, for example, two or more processing cores and two or more independent
disks. This redundancy eliminates any single point of failure. In general, the more
redundancy, the greater access you will have to applications, data, and supportive
services in the event of failure. In addition to hardware redundancy, the system must
210 Using High Availability Strategies