by a file or a block device residing in the configured storage. The choice of
a storage type will determine the format of the hard disk image. Storages which
present block devices (LVM, ZFS, Ceph) will require the *raw disk image format*,
-whereas files based storages (Ext4, NFS, GlusterFS) will let you to choose
+whereas files based storages (Ext4, NFS, CIFS, GlusterFS) will let you to choose
either the *raw disk image format* or the *QEMU image format*.
* the *QEMU image format* is a copy on write format which allows snapshots, and
thin provisioning of the disk image.
* the *raw disk image* is a bit-to-bit image of a hard disk, similar to what
you would get when executing the `dd` command on a block device in Linux. This
- format do not support thin provisioning or snapshots by itself, requiring
+ format does not support thin provisioning or snapshots by itself, requiring
cooperation from the storage layer for these tasks. It may, however, be up to
10% faster than the *QEMU image format*. footnote:[See this benchmark for details
http://events.linuxfoundation.org/sites/events/files/slides/CloudOpen2013_Khoa_Huynh_v3.pdf]
execution on the host system. If you're not sure about the workload of your VM,
it is usually a safe bet to set the number of *Total cores* to 2.
-NOTE: It is perfectly safe to set the _overall_ number of total cores in all
-your VMs to be greater than the number of of cores you have on your server (i.e.
-4 VMs with each 4 Total cores running in a 8 core machine is OK) In that case
-the host system will balance the Qemu execution threads between your server
-cores just like if you were running a standard multithreaded application.
-However {pve} will prevent you to allocate on a _single_ machine more vcpus than
-physically available, as this will only bring the performance down due to the
-cost of context switches.
+NOTE: It is perfectly safe if the _overall_ number of cores of all your VMs
+is greater than the number of cores on the server (e.g., 4 VMs with each 4
+cores on a machine with only 8 cores). In that case the host system will
+balance the Qemu execution threads between your server cores, just like if you
+were running a standard multithreaded application. However, {pve} will prevent
+you from assigning more virtual CPU cores than physically available, as this will
+only bring the performance down due to the cost of context switches.
+
+[[qm_cpu_resource_limits]]
+Resource Limits
+^^^^^^^^^^^^^^^
+
+In addition to the number of virtual cores, you can configure how much resources
+a VM can get in relation to the host CPU time and also in relation to other
+VMs.
+With the *cpulimit* (``Host CPU Time'') option you can limit how much CPU time
+the whole VM can use on the host. It is a floating point value representing CPU
+time in percent, so `1.0` is equal to `100%`, `2.5` to `250%` and so on. If a
+single process would fully use one single core it would have `100%` CPU Time
+usage. If a VM with four cores utilizes all its cores fully it would
+theoretically use `400%`. In reality the usage may be even a bit higher as Qemu
+can have additional threads for VM peripherals besides the vCPU core ones.
+This setting can be useful if a VM should have multiple vCPUs, as it runs a few
+processes in parallel, but the VM as a whole should not be able to run all
+vCPUs at 100% at the same time. Using a specific example: lets say we have a VM
+which would profit from having 8 vCPUs, but at no time all of those 8 cores
+should run at full load - as this would make the server so overloaded that
+other VMs and CTs would get to less CPU. So, we set the *cpulimit* limit to
+`4.0` (=400%). If all cores do the same heavy work they would all get 50% of a
+real host cores CPU time. But, if only 4 would do work they could still get
+almost 100% of a real core each.
+
+NOTE: VMs can, depending on their configuration, use additional threads e.g.,
+for networking or IO operations but also live migration. Thus a VM can show up
+to use more CPU time than just its virtual CPUs could use. To ensure that a VM
+never uses more CPU time than virtual CPUs assigned set the *cpulimit* setting
+to the same value as the total core count.
+
+The second CPU resource limiting setting, *cpuunits* (nowadays often called CPU
+shares or CPU weight), controls how much CPU time a VM gets in regards to other
+VMs running. It is a relative weight which defaults to `1024`, if you increase
+this for a VM it will be prioritized by the scheduler in comparison to other
+VMs with lower weight. E.g., if VM 100 has set the default 1024 and VM 200 was
+changed to `2048`, the latter VM 200 would receive twice the CPU bandwidth than
+the first VM 100.
+
+For more information see `man systemd.resource-control`, here `CPUQuota`
+corresponds to `cpulimit` and `CPUShares` corresponds to our `cpuunits`
+setting, visit its Notes section for references and implementation details.
+
+CPU Type
+^^^^^^^^
Qemu can emulate a number different of *CPU types* from 486 to the latest Xeon
processors. Each new processor generation adds new features, like hardware
but is guaranteed to work everywhere.
In short, if you care about live migration and moving VMs between nodes, leave
-the kvm64 default. If you don’t care about live migration, set the CPU type to
-host, as in theory this will give your guests maximum performance.
+the kvm64 default. If you don’t care about live migration or have a homogeneous
+cluster where all nodes have the same CPU, set the CPU type to host, as in
+theory this will give your guests maximum performance.
-You can also optionally emulate a *NUMA* architecture in your VMs. The basics of
-the NUMA architecture mean that instead of having a global memory pool available
-to all your cores, the memory is spread into local banks close to each socket.
+Meltdown / Spectre related CPU flags
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+There are two CPU flags related to the Meltdown and Spectre vulnerabilities
+footnote:[Meltdown Attack https://meltdownattack.com/] which need to be set
+manually unless the selected CPU type of your VM already enables them by default.
+
+The first, called 'pcid', helps to reduce the performance impact of the Meltdown
+mitigation called 'Kernel Page-Table Isolation (KPTI)', which effectively hides
+the Kernel memory from the user space. Without PCID, KPTI is quite an expensive
+mechanism footnote:[PCID is now a critical performance/security feature on x86
+https://groups.google.com/forum/m/#!topic/mechanical-sympathy/L9mHTbeQLNU].
+
+The second CPU flag is called 'spec-ctrl', which allows an operating system to
+selectively disable or restrict speculative execution in order to limit the
+ability of attackers to exploit the Spectre vulnerability.
+
+There are two requirements that need to be fulfilled in order to use these two
+CPU flags:
+
+* The host CPU(s) must support the feature and propagate it to the guest's virtual CPU(s)
+* The guest operating system must be updated to a version which mitigates the
+ attacks and is able to utilize the CPU feature
+
+In order to use 'spec-ctrl', your CPU or system vendor also needs to provide a
+so-called ``microcode update'' footnote:[You can use `intel-microcode' /
+`amd-microcode' from Debian non-free if your vendor does not provide such an
+update. Note that not all affected CPUs can be updated to support spec-ctrl.]
+for your CPU.
+
+To check if the {pve} host supports PCID, execute the following command as root:
+
+----
+# grep ' pcid ' /proc/cpuinfo
+----
+
+If this does not return empty your host's CPU has support for 'pcid'.
+
+To check if the {pve} host supports spec-ctrl, execute the following command as root:
+
+----
+# grep ' spec_ctrl ' /proc/cpuinfo
+----
+
+If this does not return empty your host's CPU has support for 'spec-ctrl'.
+
+If you use `host' or another CPU type which enables the desired flags by
+default, and you updated your guest OS to make use of the associated CPU
+features, you're already set.
+
+Otherwise you need to set the desired CPU flag of the virtual CPU, either by
+editing the CPU options in the WebUI, or by setting the 'flags' property of the
+'cpu' option in the VM configuration file.
+
+NUMA
+^^^^
+You can also optionally emulate a *NUMA*
+footnote:[https://en.wikipedia.org/wiki/Non-uniform_memory_access] architecture
+in your VMs. The basics of the NUMA architecture mean that instead of having a
+global memory pool available to all your cores, the memory is spread into local
+banks close to each socket.
This can bring speed improvements as the memory bus is not a bottleneck
anymore. If your system has a NUMA architecture footnote:[if the command
`numactl --hardware | grep available` returns more than one node, then your host
system has a NUMA architecture] we recommend to activate the option, as this
-will allow proper distribution of the VM resources on the host system. This
-option is also required in {pve} to allow hotplugging of cores and RAM to a VM.
+will allow proper distribution of the VM resources on the host system.
+This option is also required to hot-plug cores or RAM in a VM.
If the NUMA option is used, it is recommended to set the number of sockets to
the number of sockets of the host system.
+vCPU hot-plug
+^^^^^^^^^^^^^
+
+Modern operating systems introduced the capability to hot-plug and, to a
+certain extent, hot-unplug CPUs in a running systems. Virtualisation allows us
+to avoid a lot of the (physical) problems real hardware can cause in such
+scenarios.
+Still, this is a rather new and complicated feature, so its use should be
+restricted to cases where its absolutely needed. Most of the functionality can
+be replicated with other, well tested and less complicated, features, see
+xref:qm_cpu_resource_limits[Resource Limits].
+
+In {pve} the maximal number of plugged CPUs is always `cores * sockets`.
+To start a VM with less than this total core count of CPUs you may use the
+*vpus* setting, it denotes how many vCPUs should be plugged in at VM start.
+
+Currently only this feature is only supported on Linux, a kernel newer than 3.10
+is needed, a kernel newer than 4.7 is recommended.
+
+You can use a udev rule as follow to automatically set new CPUs as online in
+the guest:
+
+----
+SUBSYSTEM=="cpu", ACTION=="add", TEST=="online", ATTR{online}=="0", ATTR{online}="1"
+----
+
+Save this under /etc/udev/rules.d/ as a file ending in `.rules`.
+
+Note: CPU hot-remove is machine dependent and requires guest cooperation.
+The deletion command does not guarantee CPU removal to actually happen,
+typically it's a request forwarded to guest using target dependent mechanism,
+e.g., ACPI on x86/amd64.
+
[[qm_memory]]
Memory
host.
.Fixed Memory Allocation
-[thumbnail="gui-create-vm-memory-fixed.png"]
+[thumbnail="gui-create-vm-memory.png"]
-When choosing a *fixed size memory* {pve} will simply allocate what you
-specify to your VM.
+When setting memory and minimum memory to the same amount
+{pve} will simply allocate what you specify to your VM.
Even when using a fixed memory size, the ballooning device gets added to the
VM, because it delivers useful information such as how much memory the guest
really uses.
In general, you should leave *ballooning* enabled, but if you want to disable
it (e.g. for debugging purposes), simply uncheck
-*Ballooning* or set
+*Ballooning Device* or set
balloon: 0
in the configuration.
.Automatic Memory Allocation
-[thumbnail="gui-create-vm-memory-dynamic.png", float="left"]
// see autoballoon() in pvestatd.pm
-When choosing to *automatically allocate memory*, {pve} will make sure that the
+When setting the minimum memory lower than memory, {pve} will make sure that the
minimum amount you specified is always available to the VM, and if RAM usage on
the host is below 80%, will dynamically add memory to the guest up to the
maximum memory specified.
the Qemu user networking stack, where a built-in router and DHCP server can
provide network access. This built-in DHCP will serve addresses in the private
10.0.2.0/24 range. The NAT mode is much slower than the bridged mode, and
-should only be used for testing.
+should only be used for testing. This mode is only available via CLI or the API,
+but not via the WebUI.
You can also skip adding a network device when creating a VM by selecting *No
network device*.
* *Start/Shutdown order*: Defines the start order priority. E.g. set it to 1 if
you want the VM to be the first to be started. (We use the reverse startup
order for shutdown, so a machine with a start order of 1 would be the last to
-be shut down)
+be shut down). If multiple VMs have the same order defined on a host, they will
+additionally be ordered by 'VMID' in ascending order.
* *Startup delay*: Defines the interval between this VM start and subsequent
VMs starts . E.g. set it to 240 if you want to wait 240 seconds before starting
other VMs.
* *Shutdown timeout*: Defines the duration in seconds {pve} should wait
for the VM to be offline after issuing a shutdown command.
-By default this value is set to 60, which means that {pve} will issue a
-shutdown request, wait 60s for the machine to be offline, and if after 60s
-the machine is still online will notify that the shutdown action failed.
+By default this value is set to 180, which means that {pve} will issue a
+shutdown request and wait 180 seconds for the machine to be offline. If
+the machine is still online after the timeout it will be stopped forcefully.
NOTE: VMs managed by the HA stack do not follow the 'start on boot' and
'boot order' options currently. Those VMs will be skipped by the startup and
stopped.
Please note that machines without a Start/Shutdown order parameter will always
-start after those where the parameter is set, and this parameter only
-makes sense between the machines running locally on a host, and not
+start after those where the parameter is set. Further, this parameter can only
+be enforced between virtual machines running on the same host, not
cluster-wide.
Suppose you created a Debian/Ubuntu disk image with the 'vmdebootstrap' tool:
vmdebootstrap --verbose \
- --size 10G --serial-console \
+ --size 10GiB --serial-console \
--grub --no-extlinux \
--package openssh-server \
--package avahi-daemon \
The VM is ready to be started.
+
+ifndef::wiki[]
+include::qm-cloud-init.adoc[]
+endif::wiki[]
+
+
+
Managing Virtual Machines with `qm`
------------------------------------
no longer running.
+ifdef::wiki[]
+
+See Also
+~~~~~~~~
+
+* link:/wiki/Cloud-Init_Support[Cloud-Init Support]
+
+endif::wiki[]
+
+
ifdef::manvolnum[]
Files
projects / pve-docs.git / blobdiff