Recovery Manager Advanced Techniques - Oracle 10g/11g Data and Database Management Utilities - page 106

Some issues you should keep in mind when performing this kind of backup:
• The ile size should be bigger than the section size; otherwise RMAN won't
use multi section backups
• A backup set always includes the whole dataile, regardless of whether it was
produced by multi section backup or not
• If RMAN determines that more than 256 sections will be produced, then
RMAN adjusts the section size to meet this maximum
• The last section size may be less or equal than the deined backup section
Block media recovery
Block media recovery is a powerful and very practical RMAN feature. This feature
allows the DBA to recover from the dreaded ORA-01578 ORACLE data block
corrupted (file # <fileNo>, block # <blockNo>) error. In order for RMAN to
be successful in recovering from this error, some conditions must be met:
• The database must be in archivelog mode.
• You must have a full database backup. A level 1 incremental backup is not
supported in this scenario because in a missing archivelog scenario the
recovery process would fail.
• If lashback is enabled, RMAN can look for valid block copies, making the
recovery process faster.
In the following example, some blocks were corrupted at datafile 5. The corruptions
were created using the Unix command dd . When querying the database looking for
data using a regular SELECT SQL command, the ORA-01578 error shows up:
SQL> select * from employees;
select * from employees
*
ERROR at line 1:
ORA-01578: ORACLE data block corrupted (file # 5, block # 84)
ORA-01110: data file 5: '/u01/oracle/oradata/beta/example01.dbf'
SQL> select * from departments;
select * from departments
*
ERROR at line 1:
ORA-01578: ORACLE data block corrupted (file # 5, block # 56)
ORA-01110: data file 5: '/u01/oracle/oradata/beta/example01.dbf'