How to create Redo Log Groups and Members on filesystem and ASM Diskgroup

Create Redo Log member with a specific group number

on Filesystem

ALTER DATABASE ADD LOGFILE GROUP 1('/d01/oradata/orasbt1/redo1a.log', '/d02/oradata/orasbt1/redo1b.log') SIZE 20M;

on ASM Diskgroup

ALTER DATABASE ADD LOGFILE GROUP 1('+REDO', '+REDO') SIZE 20M; -- 2 members will be created on REDO disk group

Create new Redo Log members for an existing group

on Filesystem

ALTER DATABASE ADD LOGFILE MEMBER '/d03/oradata/orasbt1/redo1c.log' TO GROUP 1;

on ASM Diskgroup

ALTER DATABASE ADD LOGFILE MEMBER '+REDO' TO GROUP 1;

Notice that filenames must be specified, but sizes need not be. The size of the new members is determined from the size of the existing members of the group.