Virtualization limits for Ubuntu Server 14.04 LTS with KVM?

Question

Essentially I'm after something like this:

Virtualization limits for Red Hat Enterprise Linux with KVM

but for Ubuntu Server 14.04 LTS.

I'm trying to create some KVM guests with very large 1TB+ RAM (through OpenStack Nova). I can boot the 1TB VM fine, but I get a kernel panic with the 2TB flavor. Just wondering if I'm running into a kernel limit with the Ubuntu KVM implementation, like the 2TB limit for RHEL6.3?

Answer 1

According to the community wiki (https://help.ubuntu.com/community/32bit_and_64bit), Ubuntu itself is limited to about 1TB of memory. I would assume this means that it has trouble assigning more memory than that to a guest OS.

Answer 2

The version of Qemu shipped with Ubuntu, up to and including Bionic, doesn't support > 1TB of guest RAM. It looks like some more patches are needed that haven't gone upstream. I have opened LP: #1769053 to track the progress:

There are also CPU limits: you can have up to 255 vCPUs, and you can verify this with:

virsh maxvcpus

To look at KVM specifically, you can do virsh maxvcpus kvm - both should print 255.