Virtualization and HotPlugging/swapping

[Oliver Falk]

Am 21.01.2011 12:04, schrieb Daniel P. Berrange:
> On Thu, Jan 20, 2011 at 01:53:25PM -0600, Renich Bon Ciric wrote:
>> Hello guys!
>>
>> I'm in direct contact with the guys @ CloudSigma.
>>
>> I've asked them to support CPU, RAM and HDD hot swapping and they say
>> their system is capable of this but that linux (particularly, Fedora)
>> isn't.
>>
>> They agree to do some testing on the subject but, honestly, I don't
>> consider myself to be sufficiently knowledgeable to lead this.
>>
>> Is there anybody here interested on this?
>>
>> Anyway, their lead dev told them this:
>>
>> "Libvirt doesn't do any of this stuff itself (hot swapping). What it
>> does include is
>> an ability to use the virtio balloon driver. This essentially allows you to
>> give a guest a large amount of ram, with it then voluntarily lending some of
>> that memory back to the system. It requires a degree of cooperation and
>> trust between host and guest that isn't appropriate (or easy to bill) in a
>> public cloud, but it's a useful hack on private VM deployments in the
>> absence of proper memory hotswap in qemu-kvm."
>
> That is correct. The live memory adjustment for KVM/QEMU via
> libvirt is ballooning, not memory hotplug. Likewise for Xen
> and VMWare. Real memory hotplug is a future RFE.
>
>> I've read some stuff here:
>> http://www.linux-kvm.org/page/CPUHotPlug
>
> Yep, CPU hotplug is available for KVM/libvirt, but support among
> common guest OS is flakey. It doesn't work at all for Windows,
> and for Linux only hotplug works, but not unplug. Xen however
> did allow hot-unplug because it was using a different mechanism
> IIUC.
>
> For KVM, HDD hotplug already works for virtio disks, or SCSI
> disks, or USB disks. It doesn't work for IDE disks. For Xen
> hotplug works for xen paravirt disks.
>
> For KVM, NIC hotplug also works, and in general any kind of
> emulated PCI device can be hotplugged. For Xen, again their
> xen paravirt NICs could be hotplugged.

Erm. I'm really quite sure, I have hotplugged CPUs within my VMWare 
env... I will do a test again for both CPU and memory and tell you the 
results.

-of