IBM 990 - Manual (Page 169)

Chapter 7. Sysplex functions 157
z/OS and OS/390 software components allow new software releases to coexist with lower
levels of that software component to facilitate rolling maintenance.
Business applications are “data sharing enabled” and cloned across images to allow
workload balancing and to prevent loss of application availability in the event of an outage.
Many operational and recovery processes can be automated, reducing the need for
human intervention.
Parallel Sysplex is a way of managing a multi-system environment, providing the benefits of:
Continuous (application) availability
High capacity
Dynamic workload balancing
Simplified systems management
Resource sharing
Single system image
Continuous (application) availability
Within a Parallel Sysplex cluster, it is possible to construct a parallel processing environment
with high availability. This environment is composed of multiple images that provide
concurrent access to all critical applications and data.
You can introduce changes (such as software upgrades) one image at a time, while remaining
images continue to process work. This allows you to roll changes through your images at a
pace that makes sense for your business.
High capacity
The Parallel Sysplex environment can scale, in a nearly linear fashion, from two to 32 images.
This can be a mix of any server or operating system that supports the Parallel Sysplex
environment. The aggregated capacity of this configuration meets every processing
requirement known today.
Dynamic workload balancing
The entire Parallel Sysplex cluster can be viewed as a single logical resource to end users
and business applications. Work can be directed to any like operating system image in a
Parallel Sysplex cluster having available capacity. This avoids the need to partition data or
applications among individual images in the cluster or to replicate databases across multiple
servers.
Workload management permits you to run diverse applications across a Parallel Sysplex
cluster while maintaining the response levels critical to your business. You select the service
level agreements required for each workload, and the z/OS or OS/390 Workload Manager
(WLM), along with the subsystems such as CP/SM or WebSphere, automatically balances
tasks across all the resources of the Parallel Sysplex cluster to meet your business goals.
Whether the work is coming from batch, SNA, TCP/IP, DRDA®, or MQSeries®
(non-persistent) messages, dynamic session balancing gets the business requests into the
system best able to process the transaction. This provides the performance and flexibility you
need to achieve the responsiveness your customers demand, and it is invisible to users.