By default the BACKUP command in RMAN creates BackupSet(s) -- each of which is one or more BackupPiece(s). A datafile may span BackupPieces but may not span a BackupSet.
However, RMAN does allow another method -- BACKUP AS COPY. This is akin to "User Managed Backups" created with OS commands -- except that the ALTER TABLESPACE | DATABASE BEGIN BACKUP command does not have to be issued.
BACKUP AS COPY creates a byte-for-byte copy of each datafile [except, inasmuch, blocks being modified by concurrent writes to the datafile].
If an active datafile is corrupted, the DBA can choose to SWITCH TO COPY instead of having to restore the datafile copy. Thus, a switch can be a fast operation. Obviously, the DBA must plan carefully where he creates such copies if he intends to SWITCH anytime later (he wouldn't keep a datafile copy on a non-protected [RAID or ASM] storage target).
Here's a simple demo :
However, RMAN does allow another method -- BACKUP AS COPY. This is akin to "User Managed Backups" created with OS commands -- except that the ALTER TABLESPACE | DATABASE BEGIN BACKUP command does not have to be issued.
BACKUP AS COPY creates a byte-for-byte copy of each datafile [except, inasmuch, blocks being modified by concurrent writes to the datafile].
If an active datafile is corrupted, the DBA can choose to SWITCH TO COPY instead of having to restore the datafile copy. Thus, a switch can be a fast operation. Obviously, the DBA must plan carefully where he creates such copies if he intends to SWITCH anytime later (he wouldn't keep a datafile copy on a non-protected [RAID or ASM] storage target).
Here's a simple demo :
SQL> select file_id, file_name
2 from dba_data_files
3 where tablespace_name = 'ADD_TBS';
FILE_ID FILE_NAME
---------- ----------------------------------------
14 /oradata/orcl/add_tbs_01.dbf
SQL> alter tablespace add_tbs
2 add datafile '/oradata/orcl/add_tbs_02.dbf' size 100M;
Tablespace altered.
SQL>
SQL> create table hemant.add_table tablespace add_tbs as select * from dba_source;
Table created.
SQL> select file_id, count(*)
2 from dba_Extents
3 where owner = 'HEMANT'
4 and segment_name = 'ADD_TABLE'
5 group by file_id
6 order by 1
7 /
FILE_ID COUNT(*)
---------- ----------
14 48
15 37
SQL>
I now take backups of the two datafiles.
RMAN> backup as copy datafile 14 format '/tmp/ADDTBS01.DBF';
Starting backup at 03-JUN-12
using target database control file instead of recovery catalog
allocated channel: ORA_DISK_1
channel ORA_DISK_1: SID=13 device type=DISK
channel ORA_DISK_1: starting datafile copy
input datafile file number=00014 name=/oradata/orcl/add_tbs_01.dbf
output file name=/tmp/ADDTBS01.DBF tag=TAG20120603T224508 RECID=5 STAMP=785025915
channel ORA_DISK_1: datafile copy complete, elapsed time: 00:00:07
Finished backup at 03-JUN-12
Starting Control File Autobackup at 03-JUN-12
piece handle=/home/oracle/app/oracle/flash_recovery_area/ORCL/autobackup/2012_06_03/o1_mf_n_785025915_7wpy3vt1_.bkp comment=NONE
Finished Control File Autobackup at 03-JUN-12
RMAN> backup as copy datafile 15 format '/tmp/add_tbs_second.dbf' ;
Starting backup at 03-JUN-12
using channel ORA_DISK_1
channel ORA_DISK_1: starting datafile copy
input datafile file number=00015 name=/oradata/orcl/add_tbs_02.dbf
output file name=/tmp/add_tbs_second.dbf tag=TAG20120603T224538 RECID=6 STAMP=785025939
channel ORA_DISK_1: datafile copy complete, elapsed time: 00:00:01
Finished backup at 03-JUN-12
Starting Control File Autobackup at 03-JUN-12
piece handle=/home/oracle/app/oracle/flash_recovery_area/ORCL/autobackup/2012_06_03/o1_mf_n_785025940_7wpy4n49_.bkp comment=NONE
Finished Control File Autobackup at 03-JUN-12
RMAN>
RMAN> list backup of tablespace add_tbs completed after "sysdate-1";
specification does not match any backup in the repository
RMAN> list backup of datafile 14;
List of Backup Sets
===================
BS Key Type LV Size Device Type Elapsed Time Completion Time
------- ---- -- ---------- ----------- ------------ ---------------
18 Full 530.30M DISK 00:01:44 23-MAR-12
BP Key: 18 Status: AVAILABLE Compressed: YES Tag: TAG20120323T231454
Piece Name: /home/oracle/app/oracle/flash_recovery_area/ORCL/backupset/2012_03_23/o1_mf_nnndf_TAG20120323T231454_7ps4vgmf_.bkp
List of Datafiles in backup set 18
File LV Type Ckp SCN Ckp Time Name
---- -- ---- ---------- --------- ----
14 Full 5192430 23-MAR-12 /oradata/orcl/add_tbs_01.dbf
BS Key Type LV Size Device Type Elapsed Time Completion Time
------- ---- -- ---------- ----------- ------------ ---------------
21 Full 530.70M DISK 00:01:23 23-MAR-12
BP Key: 21 Status: AVAILABLE Compressed: YES Tag: TAG20120323T235528
Piece Name: /home/oracle/app/oracle/flash_recovery_area/ORCL/backupset/2012_03_23/o1_mf_nnndf_TAG20120323T235528_7ps77jf2_.bkp
List of Datafiles in backup set 21
File LV Type Ckp SCN Ckp Time Name
---- -- ---- ---------- --------- ----
14 Full 5194695 23-MAR-12 /oradata/orcl/add_tbs_01.dbf
BS Key Type LV Size Device Type Elapsed Time Completion Time
------- ---- -- ---------- ----------- ------------ ---------------
24 Full 1.23M DISK 00:00:00 24-MAR-12
BP Key: 24 Status: AVAILABLE Compressed: NO Tag: TAG20120324T001527
Piece Name: /home/oracle/app/oracle/flash_recovery_area/ORCL/backupset/2012_03_24/o1_mf_nnndf_TAG20120324T001527_7ps8dzm8_.bkp
List of Datafiles in backup set 24
File LV Type Ckp SCN Ckp Time Name
---- -- ---- ---------- --------- ----
14 Full 5196666 24-MAR-12 /oradata/orcl/add_tbs_01.dbf
BS Key Type LV Size Device Type Elapsed Time Completion Time
------- ---- -- ---------- ----------- ------------ ---------------
29 Full 487.60M DISK 00:00:00 01-JAN-12
BP Key: 29 Status: AVAILABLE Compressed: YES Tag: TAG20120101T112516
Piece Name: /newmountpoint/FRA/2012_01_01/o1_mf_nnndf_TAG20120101T112516_7hznjx24_.bkp
List of Datafiles in backup set 29
File LV Type Ckp SCN Ckp Time Name
---- -- ---- ---------- --------- ----
14 Full 4956816 01-JAN-12 /oradata/orcl/add_tbs_01.dbf
RMAN>
RMAN> list copy of datafile 14;
List of Datafile Copies
=======================
Key File S Completion Time Ckp SCN Ckp Time
------- ---- - --------------- ---------- ---------------
5 14 A 03-JUN-12 5353830 03-JUN-12
Name: /tmp/ADDTBS01.DBF
Tag: TAG20120603T224508
4 14 A 24-MAR-12 5196322 24-MAR-12
Name: /home/oracle/app/oracle/oradata/orcl/add_tbs.dbf
RMAN> list copy of datafile 15;
List of Datafile Copies
=======================
Key File S Completion Time Ckp SCN Ckp Time
------- ---- - --------------- ---------- ---------------
6 15 A 03-JUN-12 5353869 03-JUN-12
Name: /tmp/add_tbs_second.dbf
Tag: TAG20120603T224538
RMAN>
SQL> !rm /oradata/orcl/add_tbs_0[1-2].dbf
SQL> select count(*) from hemant.add_table;
COUNT(*)
----------
703021
SQL> alter system checkpoint;
System altered.
SQL> select count(*) from hemant.add_table;
COUNT(*)
----------
703021
SQL> alter system flush buffer_cache;
System altered.
SQL> select count(*) from hemant.add_table;
COUNT(*)
----------
703021
SQL> alter tablespace add_tbs offline;
Tablespace altered.
SQL> alter tablespace add_Tbs online;
alter tablespace add_Tbs online
*
ERROR at line 1:
ORA-01157: cannot identify/lock data file 14 - see DBWR trace file
ORA-01110: data file 14: '/oradata/orcl/add_tbs_01.dbf'
SQL>
Now, I do not have regular backups. Can I use the datafile copies ? YES.
RMAN> restore datafile 14;I actually restored datafile 14 to the target location but only switched datafile 15 to the copy. This is clearly evidenced by :
Starting restore at 03-JUN-12
using target database control file instead of recovery catalog
allocated channel: ORA_DISK_1
channel ORA_DISK_1: SID=16 device type=DISK
channel ORA_DISK_1: restoring datafile 00014
input datafile copy RECID=5 STAMP=785025915 file name=/tmp/ADDTBS01.DBF
destination for restore of datafile 00014: /oradata/orcl/add_tbs_01.dbf
channel ORA_DISK_1: copied datafile copy of datafile 00014
output file name=/oradata/orcl/add_tbs_01.dbf RECID=0 STAMP=0
Finished restore at 03-JUN-12
RMAN> switch datafile 15 to copy;
datafile 15 switched to datafile copy "/tmp/add_tbs_second.dbf"
RMAN>
SQL> select file_id, file_nameI can now simply recover the tablespace.
2 from dba_data_files
3 where tablespace_name = 'ADD_TBS';
FILE_ID FILE_NAME
---------- ----------------------------------------
14 /oradata/orcl/add_tbs_01.dbf
15 /tmp/add_tbs_second.dbf
SQL>
RMAN> recover tablespace add_tbs;and query it now.
Starting recover at 03-JUN-12
using channel ORA_DISK_1
starting media recovery
media recovery complete, elapsed time: 00:00:00
Finished recover at 03-JUN-12
RMAN> sql 'alter tablespace add_tbs online';
sql statement: alter tablespace add_tbs online
RMAN>
SQL> select /*+ FULL */ count(*) from hemant.add_table;I can also restore datafile 15 by using the same "AS COPY" and "SWITCH" trick.
COUNT(*)
----------
703021
SQL> alter tablespace add_tbs offline;
Tablespace altered.
SQL> alter tablespace add_tbs online;
Tablespace altered.
SQL> select /*+ FULL */ count(*) from hemant.add_table;
COUNT(*)
----------
703021
SQL>
RMAN> backup as copy datafile 15 format '/oradata/orcl/add_tbs_02.dbf' ;
Starting backup at 03-JUN-12
using channel ORA_DISK_1
channel ORA_DISK_1: starting datafile copy
input datafile file number=00015 name=/tmp/add_tbs_second.dbf
output file name=/oradata/orcl/add_tbs_02.dbf tag=TAG20120603T230025 RECID=7 STAMP=785026826
channel ORA_DISK_1: datafile copy complete, elapsed time: 00:00:01
Finished backup at 03-JUN-12
Starting Control File Autobackup at 03-JUN-12
piece handle=/home/oracle/app/oracle/flash_recovery_area/ORCL/autobackup/2012_06_03/o1_mf_n_785026826_7wpz0bxo_.bkp comment=NONE
Finished Control File Autobackup at 03-JUN-12
RMAN> sql 'alter tablespace add_tbs offline';
sql statement: alter tablespace add_tbs offline
RMAN> switch datafile 15 to copy;
datafile 15 switched to datafile copy "/oradata/orcl/add_tbs_02.dbf"
RMAN> recover tablespace add_tbs;
Starting recover at 03-JUN-12
using channel ORA_DISK_1
starting media recovery
media recovery complete, elapsed time: 00:00:00
Finished recover at 03-JUN-12
RMAN> sql 'alter tablespace add_tbs online';
sql statement: alter tablespace add_tbs online
RMAN>
SQL> select file_id, file_name
2 from dba_data_files
3 where tablespace_name = 'ADD_TBS';
FILE_ID FILE_NAME
---------- ----------------------------------------
14 /oradata/orcl/add_tbs_01.dbf
15 /oradata/orcl/add_tbs_02.dbf
SQL>
.
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