In VM2000 mode, less important guest systems which are I/O-intensive can hinder other, more important guest systems in I/O operations. This can occur when the I/O-intensive guest systems execute I/Os on the same (logical) device. It also occurs when I/Os are executed on different (logical) devices which are located on the same physical device or are connected over the same paths or can be reached via the same ports or are connected to the same channels.
IOLVM (I/O Limit for Virtual Machines) can detect conflict situations and specifically slows down I/O operations of the user’s own guest system if IO resources that are used jointly (channel, port, path, disk) exceed the specific IO limit for the guest system. The IO limit is specified as a percentage value of the average I/O throughput of the jointly used IO resource.
IOLVM only applies for disk devices.
The I/O limit for IOLVM is defined as the maximum I/O performance utilization of the VM in the MAX-IO-UTILIZATION operand in the VM2000 commands /CREATE-VM or /MODIFY-VM-ATTRIBUTES and /CREATE-VM-DEFINITION or /MODIFY-VM-DEFINITION.
In the VM2000 inquiry commands /SHOW-VM-ATTRIBUTES, /SHOW-VM-RESOURCES and /SHOW-VM-DEFINITION, the MAX-IO column shows which value is set for the maximum I/O performance utilization of the VM.