Parameter File Search Order in Oracle RAC

It is still not documented or rather poorly documented thing about "Parameter File Search Order in Oracle RAC". Even documentation release 11.2 continue to assert the following:

Oracle Database searches for your parameter file in a particular 
order depending on your platform.

On Linux and UNIX platforms, the search order is as follows:

  1. $ORACLE_HOME/dbs/spfilesid.ora
  2. $ORACLE_HOME/dbs/spfile.ora
  3. $ORACLE_HOME/dbs/initsid.ora

If you start your RAC database using srvctl or it is autostarted by clusterware during system boot, you may discover that sometimes database will seem to be started from another server parameter file than that, which must be in use according to Oracle Documentation, especially when you migrated your database from non-RAC configuration to RAC on same hardware.
In fact, which spfile will be used in such circumstance is determined by configuration information stored in OCR, namely:

oracle@srv1:~> srvctl config database -d iadb -a
cntn1 iadb1 /opt/oracle/product/10.2/db_1
cntn3 iadb2 /opt/oracle/product/10.2/db_1
DB_NAME: iadb
ORACLE_HOME: /opt/oracle/product/10.2/db_1
SPFILE: +DATA1/iadb/spfileiadb.ora
DOMAIN: null
DB_ROLE: PRIMARY
START_OPTIONS: null
POLICY:  AUTOMATIC
ENABLE FLAG: DB ENABLED

And if you start RAC database instance using sqlplus, than spfile will be used from places that specified in documentation.