Hotplug (qemu disk,nic,cpu,memory)

Proxmox support hotplugging of qemu devices

- disks (hotplug/unplug)

- nics (hotplug/unplug)

- cpu (hotplug/unplug)

- memory (hotplug/unplug)

Linux Guests notes

kernel modules needed

you need to have 2 modules loaded in your linux guest

#modprobe acpiphp
#modprobe pci_hotplug

cpu && memory hotplug

you need a recent kernel > 3.10

and a udev rules, to auto enable cpus or memory hotplugged

you can add a file:

/lib/udev/rules.d/80-hotplug-cpu-mem.rules

SUBSYSTEM=="cpu", ACTION=="add", TEST=="online", ATTR{online}=="0", ATTR{online}="1"
SUBSYSTEM=="memory", ACTION=="add", TEST=="state", ATTR{state}=="offline", ATTR{state}="online"

for linux kernel >= 4.7,

you don't need the udev rule for memory hotplug, you only need to add this kernel parameter at boot:

memhp_default_state=online

Windows Guests notes

- Disk and nic hotplug is working out of the box for all windows versions >2003 - cpu && memory hotplug is working on > 2008 enterprise/datacenter, 2012 > standard

Disk && Nic hotplug/unplug

edit your vm configuration file

/etc/pve/qemuserver/<VMID>.conf

and add

hotplug: network,disk,....

Note: Since proxmox 3.3, hotplug option is available in GUI.

Then add/remove your disk or nics as usual.

For disk unplug, verify that your disk is not mounted in your linux guest or disabled in windows disk management.

CPU hotplug

/etc/pve/qemuserver/<VMID>.conf

and add

cores: 2
sockets: 2
vcpus: 1
hotplug: cpu,...

You will start your vm with 1 cpu|cores, and you can hotplug later up to 4 cores. maxcpus = sockets * cores.

To hotplug a new vcpu (GUI not yet available in proxmox 3.4).

qm set VMID -vcpus 3

This will hotplug 2 new vcpus, for a total of 3vcpus.

Note : windows cpu hotplug is working since qemu 2.6 cpu hot unplug is working since qemu 2.7

Memory hotplug

Memory hotplug is available in proxmox 3.4.

You need to enable numa and hotplug to get it working

numa: 1
hotplug: memory,...

Then you can use the memory GUI as usual.

Memory hot-unplug

- Memory unplug don't work windows currently (<=win10 currently)

- Memory unplug can't be unstable on linux (<= kernel 4.10 currently)

for Linux memory unplug, you need have movable zone enabled in kernel config (not enabled by default on debian/ubuntu)

CONFIG_MOVABLE_NODE=YES

and

"movable_node" boot kernel parameter enabled

Here some futur kernel patches to improve unplug : http://www.spinics.net/lists/linux-mm/msg125359.html