There is no specific procedure at CA Support to backup your old data.
You can check the DB structure in the policy server administration guide :
There are basically 2 tables :
The following table describes the logging that appears in smaccesslog4,
which logs authentication and authorization activity
It contains an sm_timestamp column.
The following table describes the logging that appears in smobjlog4,
which logs administrative events.
It contains a sm_timestamp column.
You should involve your DBA to do the appropriate queries to extract the Data to prevent the impact on the running environment.
Hope it helps, Julien.