Add datafile:

As root

fdisk /dev/hda
 p
 n (to create a partition of desired size, say +10m; /dev/hda20 e.g. is created)
 p
 w
mknod /dev/hda20 b 3 20	#block device major number 3, minor 20
vi /etc/rc.d/rc.local
 add
 /usr/bin/raw /dev/raw/raw10 /dev/hda20
 /bin/chmod 600 /dev/raw/raw10
 /bin/chown oracle /dev/raw/raw10
Reboot

As oracle

ln -s /dev/raw/raw10 /u01/ora/oradata/OPS/users01.dbf
In sqlplus
  create tablespace users datafile '/u01/ora/oradata/OPS/users01.dbf' size 8256k reuse extent management local uniform size 16k;





Startup database:

. oraenv
OPS_A
sqlplus '/ as sysdba'
startup
alter database enable public thread 2;
exit

. oraenv
OPS_B
sqlplus '/ as sysdba'
startup
exit