Commit d4fcd298 authored by Guido Trotter's avatar Guido Trotter
Browse files

admin.rst: add information about maxmem/minmem

- Specify how maxmem and minmem are used at startup, failover and
- Add a paragraph about how to manually change the runtime memory, and
  what Ganeti will and won't do automatically as of version 2.6
Signed-off-by: default avatarGuido Trotter <>
Reviewed-by: default avatarRené Nussbaumer <>
parent 827ac163
......@@ -246,7 +246,8 @@ points to an address in the same subnet as the cluster itself.
The above command has the minimum required options; other options you
can give include, among others:
- The memory size (``-B memory``)
- The maximum/minimum memory size (``-B maxmem``, ``-B minmem``)
(``-B memory`` can be used to specify only one size)
- The number of virtual CPUs (``-B vcpus``)
......@@ -279,6 +280,8 @@ care::
gnt-instance remove INSTANCE_NAME
.. _instance-startup-label:
......@@ -287,6 +290,11 @@ manually start one which is currently stopped you can run::
gnt-instance startup INSTANCE_NAME
Ganeti will start an instance with up to its maximum instance memory. If
not enough memory is available Ganeti will use all the available memory
down to the instance minumum memory. If not even that amount of memory
is free Ganeti will refuse to start the instance.
Note, that this will not work when an instance is in a permanently
stopped state ``offline``. In this case, you will first have to
put it back to online mode by running::
......@@ -301,7 +309,7 @@ If you want to shut the instance down more permanently, so that it
does not require dynamically allocated resources (memory and vcpus),
after shutting down an instance, execute the following::
gnt-instance modify --ofline INSTANCE_NAME
gnt-instance modify --offline INSTANCE_NAME
.. warning:: Do not use the Xen or KVM commands directly to stop
instances. If you run for example ``xm shutdown`` or ``xm destroy``
......@@ -334,6 +342,27 @@ it's hardware resources (especially its disks and their redundancy
status), etc. This is harder to parse and is more expensive than the
list operation, but returns much more detailed information.
Changing an instance's runtime memory
Ganeti will always make sure an instance has a value between its maximum
and its minimum memory available as runtime memory. As of version 2.6
Ganeti will only choose a size different than the maximum size when
starting up, failing over, or migrating an instance on a node with less
than the maximum memory available. It won't resize other instances in
order to free up space for an instance.
If you find that you need more memory on a node any instance can be
manually resized without downtime, with the command::
gnt-instance modify -m SIZE INSTANCE_NAME
The same command can also be used to increase the memory available on an
instance, provided that enough free memory is available on its node, and
the specified size is not larger than the maximum memory size the
instance had when it was first booted (an instance will be unable to see
new memory above the maximum that was specified to the hypervisor at its
boot time, if it needs to grow further a reboot becomes necessary).
......@@ -476,6 +505,11 @@ node you can just run::
That's it. After the command completes the secondary node is now the
primary, and vice-versa.
The instance will be started with an amount of memory between its
``maxmem`` and its ``minmem`` value, depending on the free memory on its
target node, or the operation will fail if that's not possible. See
:ref:`instance-startup-label` for details.
Live migrating an instance
......@@ -489,6 +523,13 @@ The current load on the instance and its memory size will influence how
long the migration will take. In any case, for both KVM and Xen
hypervisors, the migration will be transparent to the instance.
If the destination node has less memory than the instance's current
runtime memory, but at least the instance's minimum memory available
Ganeti will automatically reduce the instance runtime memory before
migrating it, unless the ``--no-runtime-changes`` option is passed, in
which case the target node should have at least the instance's current
runtime memory free.
Moving an instance (offline)
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