.. _HA-recover:

Recovering from hardware failures
---------------------------------

If situations occur where the secondary node has been forced to take
over service because the primary node failed for some reason, it's
important to know how to recover.

Recovering from Minor Failures
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

If the primary went down because of a minor failure (overheating
trouble, faulty processor, faulty memory etc.) and the contents of the
files in :file:`/var/lib/vsm` are untouched, recovery is very simple and
fully automatic. Simply start the server and let the two VSM servers
resynchronize with eachother.

Recovering from Catastrophic Failure
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

If a catastrophic failure has occured, and no data on the disks of the
primary can be recovered, ThinLinc needs to be reinstalled and HA must
be reinitialized.

Install ThinLinc as described in :ref:`HA-install`, but before starting
the VSM server after enabling HA in the configuration file, copy the
file :file:`/var/lib/vsm/sessions` from the secondary to the primary.
That will preload the database of active sessions with more current
values on the primary.