Red Hat Bugzilla – Bug 1310458
Ovirt 3.6 uses hotplug memory independant of machine type
Last modified: 2016-03-23 08:27:59 EDT
Description of problem:
Ovirt must not use hotplug memory for older machine types. Otherwise startup will fail with messages like qemu-kvm: "-memory 'slots|maxmem'" is not supported by: pc-1.0
Version-Release number of selected component (if applicable):
Steps to Reproduce:
1. use ovirt 3.6 with cluster level 3.6
2. define VM and use older machine type e.g. rhel6.5.0 or pc-1.0
3. try to start vm
qemu fails to start.
qemu should start.
Bad XML for libvirt
<maxMemory slots="16">4294967296</maxMemory> <--- DOES NOT WORK
<type arch="x86_64" machine="pc-1.0">hvm</type>
Explanation of use case:
Not all the combinations of old machine type and a current cluster level make sense. Hotplug is a cluster level feature, enabled in 3.6. It does not "check" the machine type
If you don't want to have hotplug enabled you either disable it globally for 3.6 cluster level or use 3.5 compatibility level for a particular VM
Thanks for pointing that out. I was searching for such an option but did not find anything in WebUI. Maybe I'm missing something but
- how/where can I disable memory hotplug for a 3.6 cluster?
- or how/where can I enforce 3.5 compatibility for a single VM in a 3.6 cluster?
(In reply to Markus Stockhausen from comment #3)
> Thanks for pointing that out. I was searching for such an option but did not
> find anything in WebUI. Maybe I'm missing something but
> - how/where can I disable memory hotplug for a 3.6 cluster?
Via engine-config HotPlugMemorySupported parameter
> - or how/where can I enforce 3.5 compatibility for a single VM in a 3.6
This will only be possible in 4.0. You need to use a 3.5 cluster for now, and even in 4.0 there will likely be some exceptions
To your email - machine type describes all the "hw" of the virtual machine, related features, and also what is being tested. If the one from 3.6 doesn't work for you for any reason you have to keep at the older cluster level. Cluster defines the behavior for many features. In 3.6 hotplug ram is the only one which fails right away when using old machine, but it won't work reliably anyway even when you disable it. YMMV
let's see how it behaves in 4.0