小编给大家分享一下Oracle中基于RMAN如何实现坏块介质恢复，相信大部分人都还不怎么了解，因此分享这篇文章给大家参考一下，希望大家阅读完这篇文章后大有收获，下面让我们一起去了解一下吧！

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对于物理损坏的数据块，在有备份的情况下，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。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。本篇我们来模拟产生一个坏块，然后使用RMAN实现坏块恢复。

说明：
一般出现坏块的时候，都是业务访问到这个坏块的时候报如下的错误：
ERROR at line 1:
ORA-01578: ORACLE data block corrupted (file # 18, block # 130)
ORA-01110: data file 18: '/ora11gSource/ora11g/tbs_tmp.dbf'

操作：
1 创建用于演示的表空间  
create tablespace tbs_tmp datafile '/ora11gSource/ora11g/tbs_tmp.dbf' size 10m autoextend on;   

2 基于新的数据文件创建对象tb_tmp
conn scott/tiger;  
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
---------- ------------------------------------------------------------
        18 /ora11gSource/ora11g/tbs_tmp.dbf
  
3 表对象tb_tmp上的信息，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_N HEADER_FILE HEADER_BLOCK     BLOCKS
--------- ----------- ------------ ----------
TB_TMP             18          130       1280
  
4 使用rman对该数据文件进行一次备份
$ $ORACLE_HOME/bin/rman target /  
RMAN> backup datafile 18 tag=health;

Starting backup at 12-JUN-18
using target database control file instead of recovery catalog
allocated channel: ORA_DISK_1
channel ORA_DISK_1: SID=37 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=00018 name=/ora11gSource/ora11g/tbs_tmp.dbf
channel ORA_DISK_1: starting piece 1 at 12-JUN-18
channel ORA_DISK_1: finished piece 1 at 12-JUN-18
piece handle=/ora11gSource/zhida/ORA11G/backupset/2018_06_12/o1_mf_nnndf_HEALTH_fkz35h7r_.bkp tag=HEALTH comment=NONE
channel ORA_DISK_1: backup set complete, elapsed time: 00:00:01
Finished backup at 12-JUN-18

5 人为制造一个单块数据块的损坏
使用linux自带的dd命令来损坏单块数据块  
ora11g[redora]/home/ora11g>dd of=/ora11gSource/ora11g/tbs_tmp.dbf bs=8192 conv=notrunc seek=130 <> Corrupted block!
> EOF
0+1 records in
0+1 records out
17 bytes (17 B) copied, 5.9505e-05 seconds, 286 kB/s

6 触发坏块所在对象  
清空buffer cache 
conn scott/tiger; 
alter system flush buffer_cache;  
查询表对象 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 # 18, block # 130)
ORA-01110: data file 18: '/ora11gSource/ora11g/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
---------- ---------- ---------- ------------------ ---------
        18        130          1                  0 CORRUPT
  
7 使用dbv工具来校验坏块
ora11g[redora]/home/ora11g>dbv file=/ora11gSource/ora11g/tbs_tmp.dbf feedback=1000
DBVERIFY: Release 11.2.0.4.0 - Production on Wed Jun 13 10:25:13 2018
Copyright (c) 1982, 2011, Oracle and/or its affiliates.  All rights reserved.
DBVERIFY - Verification starting : FILE = /ora11gSource/ora11g/tbs_tmp.dbf
Page 130 is marked corrupt
Corrupt block relative dba: 0x04800082 (file 18, block 130)
Bad header found during dbv: 
Data in bad block:
 type: 67 format: 7 rdba: 0x65747075
 last change scn: 0x636f.6c622064 seq: 0x6b flg: 0x21
 spare1: 0x72 spare2: 0x72 spare3: 0x0
 consistency value in tail: 0x8d8d2301
 check value in block header: 0xc50a
 block checksum disabled
..
DBVERIFY - Verification complete
Total Pages Examined         : 1536
Total Pages Processed (Data) : 1196
Total Pages Failing   (Data) : 0
Total Pages Processed (Index): 0
Total Pages Failing   (Index): 0
Total Pages Processed (Other): 154
Total Pages Processed (Seg)  : 0
Total Pages Failing   (Seg)  : 0
Total Pages Empty            : 185
Total Pages Marked Corrupt   : 1
Total Pages Influx           : 0
Total Pages Encrypted        : 0
Highest block SCN            : 939342345 (3332.939342345)  

8 下面使用blockrecover来恢复坏块        
RMAN> blockrecover datafile 18 block 130;

Starting recover at 13-JUN-18
using channel ORA_DISK_1
searching flashback logs for block images until SCN 14311770329033
finished flashback log search, restored 1 blocks

starting media recovery
media recovery complete, elapsed time: 00:00:07

Finished recover at 13-JUN-18
  
9 验证修复效果
再次查询表tb_emp正常  
SQL> select count(*) from tb_tmp;  
  
  COUNT(*)  
----------  
     72449  

ora11g[redora]/home/ora11g>dbv file=/ora11gSource/ora11g/tbs_tmp.dbf feedback=1000
DBVERIFY: Release 11.2.0.4.0 - Production on Wed Jun 13 10:26:31 2018
Copyright (c) 1982, 2011, Oracle and/or its affiliates.  All rights reserved.
DBVERIFY - Verification starting : FILE = /ora11gSource/ora11g/tbs_tmp.dbf
..
DBVERIFY - Verification complete
Total Pages Examined         : 1536
Total Pages Processed (Data) : 1196
Total Pages Failing   (Data) : 0
Total Pages Processed (Index): 0
Total Pages Failing   (Index): 0
Total Pages Processed (Other): 155
Total Pages Processed (Seg)  : 0
Total Pages Failing   (Seg)  : 0
Total Pages Empty            : 185
Total Pages Marked Corrupt   : 0
Total Pages Influx           : 0
Total Pages Encrypted        : 0
Highest block SCN            : 939342345 (3332.939342345)

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