Linux on KVM versus Linux on z/VM or Linux in LPAR mode

6.10 KVM guest

If you are familiar with Linux® on z/VM® or with Linux in LPAR mode, you will observe some differences when working with Linux on IBM® Z as a KVM guest.

Starting and stopping Linux

The KVM hypervisor is the control point for IPL of Linux on KVM. You can initiate a reIPL from a running instance of Linux on KVM.

System dump

As for Linux in LPAR mode and for Linux on z/VM, you can use kdump as a dump tool.

Alternatively, you can initiate a dump on the host. These hypervisor-driven dumps are analogous to using VMDUMP for Linux on z/VM.

You cannot use the stand-alone dump tools to create a dump for Linux on KVM.

For more details, see Creating a kernel dump of a KVM guest.

Responsibilities

Some of the administrative powers and responsibilities for the hardware that backs devices or provides access to devices are offloaded from the guest to the host.

Virtual channel subsystem

The KVM hypervisor provides a virtualized channel subsystem with virtual channel paths to its guests. CHPID 00 on this virtual channel subsystem is shared by all virtio-ccw devices, including virtio-net and virtio-blk devices.

Storage devices

Expect to find generic block devices, which can be backed on the KVM host by SCSI disks, DASDs, PCIe-attached NVMe devices, or even files in the host file system.

For these generic block devices, you cannot and need not configure any adapter hardware or physical disk devices. This preparation is done for you by the host.

There are no storage-class memory increments.

Network devices

Expect to find generic virtio network devices, which can be backed on the KVM host by an OSA device, a HiperSockets device, a PCIe-attached Mellanox adapter, or an Open vSwitch configuration.

For these generic network devices, you cannot and need not group subchannels into CCW group devices, configure any adapter hardware, or configure the device itself. This setup is done for you by the host.