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pmxcfs: add manual guest recovery by moving files

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Fabian Grünbichler 2016-11-08 14:44:15 +01:00 committed by Dietmar Maurer
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commit 5db724de29
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@ -176,6 +176,45 @@ In some cases, you might prefer to put a node back to local mode without
reinstall, which is described in
<<pvecm_separate_node_without_reinstall,Separate A Node Without Reinstalling>>
Recovering/Moving Guests from Failed Nodes
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
For the guest configuration files in `nodes/<NAME>/qemu-server/` (VMs) and
`nodes/<NAME>/lxc/` (containers), {pve} sees the containing node `<NAME>` as
owner of the respective guest. This concept enables the usage of local locks
instead of expensive cluster-wide locks for preventing concurrent guest
configuration changes.
As a consequence, if the owning node of a guest fails (e.g., because of a power
outage, fencing event, ..), a regular migration is not possible (even if all
the disks are located on shared storage) because such a local lock on the
(dead) owning node is unobtainable. This is not a problem for HA-managed
guests, as {pve}'s High Availability stack includes the necessary
(cluster-wide) locking and watchdog functionality to ensure correct and
automatic recovery of guests from fenced nodes.
If a non-HA-managed guest has only shared disks (and no other local resources
which are only available on the failed node are configured), a manual recovery
is possible by simply moving the guest configuration file from the failed
node's directory in `/etc/pve/` to an alive node's directory (which changes the
logical owner or location of the guest).
For example, recovering the VM with ID `100` from a dead `node1` to another
node `node2` works with the following command executed when logged in as root
on any member node of the cluster:
mv /etc/pve/nodes/node1/qemu-server/100.conf /etc/pve/nodes/node2/
WARNING: Before manually recovering a guest like this, make absolutely sure
that the failed source node is really powered off/fenced. Otherwise {pve}'s
locking principles are violated by the `mv` command, which can have unexpected
consequences.
WARNING: Guest with local disks (or other local resources which are only
available on the dead node) are not recoverable like this. Either wait for the
failed node to rejoin the cluster or restore such guests from backups.
ifdef::manvolnum[]
include::pve-copyright.adoc[]
endif::manvolnum[]