I/O priority groups can be used to protect work which
is extremely I/O-sensitive. When you assign a service class to I/O
priority group HIGH, you ensure that work managed by this service
class always has a higher I/O priority than work managed by service
classes assigned to I/O priority group NORMAL which is the default
for service classes.
The default for Enabling I/O Priority Groups is no,
which will ignore I/O priority groups. If you specify yes,
you enable workload management to consider I/O priority groups and
setting higher I/O priorities for work in I/O priority group HIGH
than for work in NORMAL.