"Fast" and "slow" pool members?
I'm planning a new XCP-ng pool, where we plan on using HP Gen8 blades. These are available with a bunch of different CPU options, so I'd like to know if it would be reasonable to have e.g. half the blades with a CPU model that has fewer cores but higher clock speed, and half with a CPU with more cores and lower clock speed. All of the CPUs would be Xeon E5 26xx v2, so they should all have the same CPU features.
Would I be able to live-migrate guests between the fast and slow hosts, or would only cold-migrate be possible in this situation?
With such a setup, could I designate the slow hosts as the default for new guests? I would prefer to reserve the fast hosts for guests that actually need the higher clock speed, typically for single-thread workloads.
If you enter all hosts in a pool and all servers are up when the vm's are started you'll be able to safely live-migrate.
You can even have more different CPUs but that is not recommended. Also the CPU masking will modify with any host up or down from the pool and will have effect only at the vm start, that's why all XCP hosts should be up when starting vm's.
You'll be able to live-migrate vm's only on hosts with same CPU features as when the vm was started.
@gn_ro Will there be any CPU masking if they all have the same feature set though?
In my scenario there's only a speed difference between the CPUs, nothing else.
The pool master will calculate this when adding new hosts. If you have simillar CPUs all will be ok.
@gn_ro Great, thanks!
To answer your last question, you can sort of make this work, you can set a "home" server for each VM where it will try to start first, if home server isn't available it will start on any other available server. If you want absolute separation then you'll have to make 2 pools and split them there. You should still be able to live migrate the VMs between pools but you won't be able to share your SR between pools.