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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?

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  • 3
    My gosh... what are you doing!?!
    – ewwhite
    May 9, 2015 at 6:33
  • /usr/libexec/qemu-kvm -drive file=/root/deep-thought.img is my guess.
    – MadHatter
    Sep 8, 2015 at 15:47
  • Initially seconding ewwhite's excellent comment! and adding wouldn't this be a kernel issue? couldn't you compile Ubuntu with the Redhat kernel config? (its a passing thought, I could be way off)
    – Michael B
    Sep 8, 2015 at 15:50
  • Better yet don't use Ubuntu at all!
    – Michael Hampton
    Sep 8, 2015 at 20:43

2 Answers 2

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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.

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  • That page is really really outdated. The Linux kernel will happily address 64TB on modern hardware and Ubuntu doesn't impose any extra limits beyond that. Certainly people run it on machines with > 1TB of RAM.
    – dja
    May 4, 2018 at 5:40
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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.

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