Joined: 15 Oct 2006 Posts: 6 Location: Mooresville,NC-USA
The difference between the JES2 and JES3 is as below
JES2 processing is considered to be independently controlled. Each
JES2 image processes its own job input, job scheduling and job output.
JES2 uses a contention-based paradigm for managing a multi-image
workload. Each image ?wakes up? periodically and attempts to serialize
the JES2 checkpoint using a hardware serialization technique. The image
that succeeds carries out job and output scheduling activities. The others
go back ?to sleep? waiting for another chance. There is no cooperative
decision-making process. The order in which activities occur and on
which images is random.
By contrast, JES3 processing is considered to be centrally controlled.
One image is designated as the focal point for the entry and distribution
of jobs and for the control of resources needed by the jobs. That image,
called the global processor, distributes work to itself and the other images
in the configuration, known as local processors. It is from the global
processor that JES3 manages jobs and resources for the entire JESplex,
matching jobs with available resources. JES3 manages processors
(images), I/O devices, volumes, and data. To avoid delays that result
when these resources are not available, JES3 ensures that they are
available before selecting the job for processing. Using this centralized
approach, JES3 can make informed and complex decisions about job
scheduling and placement.