对于物理损坏的数据块，我们可以通过RMAN块介质恢复(BLOCK MEDIA RECOVERY)功能来完成受损块的恢复，而不需要恢复整个数据库或所有文件来修复这些少量受损的数据块。恢复整个数据库或数据文件那不是大炮用来打蚊子，有点不值得！但前提条件是你得有一个可用的RMAN备份存在，因此，无论何时备份就是一切。本文演示了产生坏块即使用RMAN实现坏块恢复的全过程。
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1、创建演示环境
SQL> select * from v$version where rownum create tablespace tbs_tmp datafile '/u02/database/usbo/oradata/tbs_tmp.dbf' size 10m autoextend on;
SQL> conn scott/tiger;
--基于新的数据文件创建对象tb_tmp
SQL> create table tb_tmp tablespace tbs_tmp as select * from dba_objects;
SQL> col file_name format a60
SQL> select file_id,file_name from dba_data_files where tablespace_name='TBS_TMP';
FILE_ID FILE_NAME
---------- ------------------------------------------------------------
6 /u02/database/usbo/oradata/tbs_tmp.dbf
--表对象tb_tmp上的信息，包含对应的文件信息，头部块，总块数
SQL> select segment_name , header_file , header_block,blocks
2 from dba_segments
3 where segment_name = 'TB_TMP' and owner='SCOTT';
SEGMENT_NAME HEADER_FILE HEADER_BLOCK BLOCKS
------------------------------ ----------- ------------ ----------
TB_TMP 6 130 1152
--首先使用rman备份对应的数据文件
$ $ORACLE_HOME/bin/rman target /
RMAN> backup datafile 6 tag=health;
Starting backup at 2013/08/28 17:03:15
allocated channel: ORA_DISK_1
channel ORA_DISK_1: SID=24 device type=DISK
channel ORA_DISK_1: starting full datafile backup set
channel ORA_DISK_1: specifying datafile(s) in backup set
input datafile file number=00006 name=/u02/database/usbo/oradata/tbs_tmp.dbf
channel ORA_DISK_1: starting piece 1 at 2013/08/28 17:03:16
channel ORA_DISK_1: finished piece 1 at 2013/08/28 17:03:17
piece handle=/u02/database/usbo/fr_area/USBO/backupset/2013_08_28/o1_mf_nnndf_HEALTH_91vh6ntb_.bkp tag=HEALTH comment=NONE
channel ORA_DISK_1: backup set complete, elapsed time: 00:00:01
Finished backup at 2013/08/28 17:03:17
RMAN> exit
2、单块数据块损坏的恢复处理
--下面使用了linux自带的dd命令来损坏单块数据块
[oracle@linux1 ~]$ dd of=/u02/database/usbo/oradata/tbs_tmp.dbf bs=8192 conv=notrunc seek=130 EOF
0+1 records in
0+1 records out
17 bytes (17 B) copied, 0.000184519 seconds, 92.1 kB/s
--清空buffer cache
SQL> alter system flush buffer_cache;
--查询表对相 tb_tmp,收到ORA-01578
SQL> select count(*) from tb_tmp;
select count(*) from tb_tmp
*
ERROR at line 1:
ORA-01578: ORACLE data block corrupted (file # 6, block # 130)
ORA-01110: data file 6: '/u02/database/usbo/oradata/tbs_tmp.dbf'
--查询视图v$database_block_corruption，提示有坏块，注意该视图可能不会返回任何数据，如无返回，先执行backup validate
SQL> select * from v$database_block_corruption;
FILE# BLOCK# BLOCKS CORRUPTION_CHANGE# CORRUPTIO
---------- ---------- ---------- ------------------ ---------
6 129 1 0 CORRUPT
--也可以使用dbv工具来校验坏块，参考:
--下面使用blockrecover来恢复坏块
RMAN> blockrecover datafile 6 block 130;
Starting recover at 2013/08/28 17:22:25
using target database control file instead of recovery catalog
allocated channel: ORA_DISK_1
channel ORA_DISK_1: SID=24 device type=DISK
channel ORA_DISK_1: restoring block(s)
channel ORA_DISK_1: specifying block(s) to restore from backup set
restoring blocks of datafile 00006
channel ORA_DISK_1: reading from backup piece /u02/database/usbo/fr_area/USBO/backupset/2013_08_28/o1_mf_nnndf_HEALTH_91vh6ntb_.bkp
channel ORA_DISK_1: piece handle=/u02/database/usbo/fr_area/USBO/backupset/2013_08_28/o1_mf_nnndf_HEALTH_91vh6ntb_.bkp tag=HEALTH
channel ORA_DISK_1: restored block(s) from backup piece 1
channel ORA_DISK_1: block restore complete, elapsed time: 00:00:01
starting media recovery
media recovery complete, elapsed time: 00:00:03
Finished recover at 2013/08/28 17:22:31
--再次查询表tb_emp正常
SQL> select count(*) from tb_tmp;
COUNT(*)
----------
72449