Volume Sets and Volumes for Archive (ON-Archive) 
Before you can archive the Informix database with
ON-Archive , you must define at least one volume set and volume. You can set up volume sets and volumes on tape in either of the following ways:You should use the SAP scripts if possible since they enable you to define the required volume sets and volumes, as described below.
Refer to
If you are archiving to disk (not generally recommended), or archiving in parallel then you must define the volumes yourself. Refer to