Explanation:
Command ALTER DATABASE . . ADD LOGFILE MEMBER is used for multiplexing existing online redo logs, it adds members to redo log file. Each member needs to be placed on separate disks to decrease possibility of corrupting all members of the group.
Incorrect Answers:
1: This command just creates new group, it has nothing to do with multiplexing.
3: You don't need to shut down the database to multiplex existing online redo logs.
4: You don't need to shut down the database to multiplex existing online redo logs.
Oracle 8, DBA Certification Exam Guide, Jason S. Couchman, p. 572-574
Chapter 12: Overview of Backup and Recovery

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