Oracle中基于RMAN如何实现坏块介质恢复
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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
$ $ORACLE_HOME/bin/rman target /
RMAN> backup datafile 18 tag=health;
Starting backup at 12-JUN-18
using target database control file instead of recovery catalog
allocated channel: ORA_DISK_1
channel ORA_DISK_1: SID=37 device type=DISK
channel ORA_DISK_1: starting full datafile backup set
channel ORA_DISK_1: specifying datafile(s) in backup set
input datafile file number=00018 name=/ora11gSource/ora11g/tbs_tmp.dbf
channel ORA_DISK_1: starting piece 1 at 12-JUN-18
channel ORA_DISK_1: finished piece 1 at 12-JUN-18
piece handle=/ora11gSource/zhida/ORA11G/backupset/2018_06_12/o1_mf_nnndf_HEALTH_fkz35h7r_.bkp tag=HEALTH comment=NONE
channel ORA_DISK_1: backup set complete, elapsed time: 00:00:01
Finished backup at 12-JUN-18
5 人为制造一个单块数据块的损坏
使用linux自带的dd命令来损坏单块数据块
ora11g[redora]/home/ora11g>dd of=/ora11gSource/ora11g/tbs_tmp.dbf bs=8192 conv=notrunc seek=130 <
> EOF
0+1 records in
0+1 records out
17 bytes (17 B) copied, 5.9505e-05 seconds, 286 kB/s
6 触发坏块所在对象
清空buffer cache
conn scott/tiger;
alter system flush buffer_cache;
查询表对象 tb_tmp,收到ORA-01578
SQL> select count(*) from tb_tmp;
select count(*) from tb_tmp
*
ERROR at line 1:
ORA-01578: ORACLE data block corrupted (file # 18, block # 130)
ORA-01110: data file 18: '/ora11gSource/ora11g/tbs_tmp.dbf'
查询视图v$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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