How to simulate block corruption and do RMAN block recovery

RMAN offers a blockrecover command to recover from a block corruption.Otherwise we would have to restore the entire datafile and thereby recover it.

Lets simulate block media recovery

1) Corrupt datafile users.dbf for instance

$ dd if=/dev/zero of=/u/oracle/oradata/test/users.dbf bs=8k conv=notrunc seek=20 count=1

2) verify the block corruption using dbverify utility:

$dbv file=/u/oracle/oradata/test/users.dbf blocksize=8192

DBVERIFY: Release 10.2.0.1.0 - Production on Tue Jul 20 16:21:06 2010

Copyright (c) 1982, 2005, Oracle.  All rights reserved.

DBVERIFY - Verification starting : FILE = /u/oracle/oradata/test/users.dbf
Page 20 is marked corrupt
Corrupt block relative dba: 0x01000014 (file 4, block 20)
Completely zero block found during dbv:

DBVERIFY - Verification complete

Total Pages Examined         : 131072
Total Pages Processed (Data) : 87614
Total Pages Failing   (Data) : 0
Total Pages Processed (Index): 5449
Total Pages Failing   (Index): 0
Total Pages Processed (Other): 1449
Total Pages Processed (Seg)  : 0
Total Pages Failing   (Seg)  : 0
Total Pages Empty            : 36559
Total Pages Marked Corrupt   : 1
Total Pages Influx           : 0
Highest block SCN            : 301640 (0.301640)

Block 20 of datafile 4 is corrupted.

3) Lets do RMAN block recovery using blockrecover command.

RMAN> blockrecover datafile 4 block 20;

Starting blockrecover at 20-JUL-10
using channel ORA_DISK_1

channel ORA_DISK_1: restoring block(s)
channel ORA_DISK_1: specifying block(s) to restore from backup set
restoring blocks of datafile 00004
channel ORA_DISK_1: reading from backup piece /u1/flash_recovery_area/test/backupset/2010_07_16/o1_mf_nnndf_TAG20100716T181457_640o2b16_.bkp
channel ORA_DISK_1: restored block(s) from backup piece 1
piece handle=/u1/flash_recovery_area/test/backupset/2010_07_16/o1_mf_nnndf_TAG20100716T181457_640o2b16_.bkp tag=TAG20100716T181457
channel ORA_DISK_1: block restore complete, elapsed time: 00:00:45

starting media recovery

archive log thread 1 sequence 17 is already on disk as file /u1/flash_recovery_area/test/archivelog/2010_07_17/o1_mf_1_17_642q4zbv_.arc
archive log thread 1 sequence 18 is already on disk as file /u1/flash_recovery_area/test/archivelog/2010_07_19/o1_mf_1_18_647vt1ps_.arc
archive log thread 1 sequence 19 is already on disk as file /u1/flash_recovery_area/test/archivelog/2010_07_19/o1_mf_1_19_647vvqrz_.arc
archive log thread 1 sequence 20 is already on disk as file /u1/flash_recovery_area/test/archivelog/2010_07_20/o1_mf_1_20_64byfgff_.arc
archive log thread 1 sequence 21 is already on disk as file /u1/flash_recovery_area/test/archivelog/2010_07_20/o1_mf_1_21_64byfgjf_.arc
archive log thread 1 sequence 22 is already on disk as file /u1/flash_recovery_area/test/archivelog/2010_07_20/o1_mf_1_22_64byfg8f_.arc
media recovery complete, elapsed time: 00:00:05
Finished blockrecover at 20-JUL-10