z/VM SSI: make your Linux relocatable

Virtualization systems like KVM, Xen, or z/VM offer the possibility to move running guests from one physical server to another one without service interruption. This is a cool feature for the system administrator because he can service a virtualization host without shutting down any workload on his cluster.

Before doing such a migration, the system perform a number of checks. Especially z/VM is very strict with this, but also gives high confidence that nothing bad happens with the workload. Unfortunately, the default system you get when running linux on z/VM has a number of devices attached, that prevent z/VM from relocating that guest to a different node. A typical message would look like this:

HCPRLH1940E LINUX001 is not relocatable for the following reason(s):
HCPRLI1996I LINUX001: Virtual machine device 0191 is a link to a local minidisk

For some of the devices it is obvious to the experienced z/VM admin that he can detach them. However some of the devices might also be in use by Linux, and it would definitly confuse the system when just removing the device. Therefore, the z/VM admin has to ask the person reponsible for Linux if it is ok to remove that device. When talking about 10 guests, this might be ok, but when talking about lots and lots of servers and many different Stakeholders, this can get quite painful.

Starting with SLES12 SP2, a new service called “virtsetup” sneaked into the system that can ease this task a lot. When enabled, it removes all the unneeded CMS disks from the guest and thus prepares the guest for live guest relocation.

How to run this service:
# systemctl enable virtsetup
# systemctl start virtsetup

Thats basically everything you have to do for a default setup. If you want some specific disk untouched, just have a look at “/etc/sysconfig/virtsetup”. This is the file where this service is configured.

Enabling this service is not a big deal for the single machine, but it makes a big difference for the z/VM admin. When this is enabled, most machines will simply be eligible for relocation without further action and thus allowing for continuous operation during service of a z/VM Node.

This entry was posted in Mainframe, SLES12, systemd, z Linux, zVM. Bookmark the permalink.

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