-> When trying to connect EMS with Oracle database and getting this error:

SEVERE ERROR: Unable to open store [$sys.failsafe]: [ ESTATUS = 230, ERRSTR = com.tibco.tibems.tibemsd.internal.db.EMSDataStoreException: failed to open store: IO Error: Unknown host specified  ]

Causes:
=======
This error means that your machine (where you are trying to connect to the database host) is unable to identify the hostname of the database server.
 

SEVERE ERROR: Unable to open store [$sys.failsafe]: [ ESTATUS = 230, ERRSTR = com.tibco.tibems.tibemsd.internal.db.EMSDataStoreException: failed to open store: IO Error: Unknown host specified ]

ALL

-> Check the hostname in dbstore_driver_url in stores.conf/stores-db.conf.

-> In a non-RAC Oracle database, a single instance accesses a single database. The database consists of a collection of data files, control files, and redo logs located on the disk.

Also, use the below format to define any Oracle database stores in stores.conf/stores-db.conf:

[$sys.failsafe]
  type=dbstore
  dbstore_driver_url=jdbc:oracle:thin:sysfailsafe/sysfailsafe@//perf3:1521/orcl
  dbstore_driver_username=sysfailsafe
  dbstore_driver_password=sysfailsafe

-> In an Oracle RAC environment, 2 or more instances concurrently access a single database. This allows an application or user to connect to either computer and have access to a single coordinated set of data. The instances are connected with each other through an "Interconnect" which enables all the instances to be in sync in accessing the data.

For Oracle RAC, use the below format to define database stores in stores.conf/stores-db.conf:

[$sys.failsafe]
   type=dbstore
   dbstore_driver_url=jdbc:oracle:oci:sysfailsafe/sysfailsafe@(DESCRIPTION=(ADDRESS=(PROTOCOL=TCP)(HOST=perf3)(PORT=1521)))(CONNECT_DATA=(SERVICE_NAME=orcl)(FAILOVER_MODE=(TYPE=SELECT)(METHOD=BASIC)(RETRIES=180)(DELAY=5))))
 dbstore_driver_username=sysfailsafe
 dbstore_driver_password=sysfailsafe

This assumes that a database by the name 'orcl' exists at host perf3. 
Also assumes that there is user sysfailsafe created.

Please refer to the EMS User's Guide:
Database Stores -> 
- Configuration in stores.conf 
- Configuration for the Oracle RAC Database