RMAN实战12：ORACLE数据块坏块的检查和恢复

数据块的故障很少见，一般是因为磁盘IO引起的，如果数量块坏块少可以执行恢复数据块的恢复，如果量大则就用数据文件或者表空间的恢复。在运行backup validate、或者backup validate命令时会进行坏块的检查。

检查数据文件和备份文件坏块的命令

• validate (仅仅支持11G和更高版本，低版本用下面两个)
• backup …validate
• restore …validate

validate

摘录一段《深入理解ORACLE 12C 数据库管理》中的一段原文：
Using VALIDATE
The VALIDATE command can be used stand-alone to check for missing files or physical corruption in database data files, archive redo log files, control files, spfiles, and backup set pieces.

 #validate all data files and the control files:RMAN> validate database;#You can also validate just the control file, as follows:RMAN> validate current controlfile;#You can validate the archive redo log files, like so:RMAN> validate archivelog all;#You may want to combine all the prior integrity checks into one command, as shown:RMAN> validate database include current controlfile plus archivelog;#Under normal conditions the VALIDATE command only checks for physical corruption. You can specify that you also want to check for logical corruption by using the CHECK LOGICAL clause:RMAN> validate check logical database include current controlfile plus archivelog;#VALIDATE has a variety of uses. Here are a few more examples:RMAN> validate database skip offline;RMAN> validate copy of database;RMAN> validate tablespace system;RMAN> validate datafile 3 block 20 to 30;RMAN> validate spfile;RMAN> validate backupset <primary_key_value>;RMAN> validate recovery area;#If you’re using the Oracle Database 12c pluggable database feature, you can validate specific databases within the container. While connected as SYS to the root container, validate any associated pluggable databases:RMAN> validate pluggable database salespdb;#If RMAN detects any corrupt blocks, the V$DATABASE_BLOCK_CORRUPTION is populated. This view contains information on the file number, block number, and number of blocks affected. You can use this information to perform a block-level recovery .

关于物理坏块和逻辑坏块的解释：

physical corruption is a change to a block, such that its contents don’t match the physical format that Oracle expects. By default, rMaN checks for physical corruption when backing up, restoring, and validating data files. With logical corruption, a block is in the correct format, but the contents aren’t consistent with what Oracle expects, such as in a row piece or an index entry.

backup …validate

这个命令和validate 命令类似，就是多个backup 开头，但是适合各种版本，不以backup开头的只能在11G及以后版本使用。列出几个常用命令。

RMAN> backup validate database;RMAN> backup validate check logical database;RMAN> backup validate database current controlfile;RMAN> backup validate check logical database current controlfile plus archivelog;

restore …validate

一般这个命令用来模拟数据库的restore，一般用来检查备份是否可以用来恢复。

RMAN> restore validate database;

坏块的恢复

用下面的这sql来查坏块:

SQL> select * from v$database_block_corruption;FILE# BLOCK# BLOCKS CORRUPTION_CHANGE# CORRUPTIO CON_ID---------- ---------- ---------- ------------------ --------- ----------4 20 1 0 ALL ZERO 0

找到后用这个命令进行恢复，数据库可以在mount或者open状态下都可以：

RMAN> recover corruption list;

也可指定恢复，一般推荐前者，可以自动清理v$database_block_corruption视图：

RMAN> recover datafile 4 block 20;