Getting Started with Server-Managed Recovery (SMR) and RMAN 8.0/8i_50875.1

Introduction:

This document explains the basic operation of SMR & RMAN. Because of the
enormous flexibility of RMAN only the most basic features will be covered
here. For more information, please read the Oracle8 Server Backup & Recovery
Guide or Oracle8i Recovery Manager User's Guide. For comprehensive examples,
please view the online case*.rcv scripts in $ORACLE_HOME/rdbms/demo.

For the sake of clarity, I have excluded RMAN error messages and return
codes unless necessary. It is usually obvious when an error occurs!
 
See also :
Note 120084.1 RMAN 8.0 to 8i - Getting Started
Note.360416.1 Oracle10g - Getting Started with Recovery Manager (RMAN)
 

Contents:

1.   What is RMAN & SMR?
2.   Terminology
3.   The recovery catalog
4.   Starting RMAN
5.   Register the target database
6.   Adding existing backups to the recovery catalog
7.   Backing up in noarchivelog mode
8.   Backing up in archivelog mode
9.   Incremental backups
10. Cumulative incremental backups
11. Checking Backup Progress
12. Recovery
13. Scripts
14. Parallelization
15. Corruption detection
16. Channels
17. Reports
18. Hints, tips,& best practices
19.  Limitations
 
 

1. What is RMAN?

RMAN can be used to backup and restore database files, archive logs, and
control files. It can also be used to perform complete or incomplete
database recovery. Note that RMAN cannot be used to backup initialization
files or password files.
 

RMAN starts Oracle server processes on the database to be backed up or
restored. The backup, restore, and recovery is driven through these processes
hence the term 'server-managed recovery'.

Note that SMR can also be controlled from OEM's Backup Manager GUI. This
article will not discuss Backup Manager.
 

2. Terminology

2.1. Backup sets

 A backup set is characterised by the following:

       - Contains one or more datafiles or archivelogs
       - Stored in an Oracle proprietary format
       - Comprises a complete set of backup pieces
       - Constitutes a full or incremental backup
 

2.2. Backup pieces

A backup set is comprised of a number of backup pieces. Each backup piece
is a single output file. The size of a backup piece can be restricted;
if the size is not restricted, the backup set will comprise one backup
piece. Backup piece size should be restricted to no larger than the
maximum file size that your filsystem will support.

2.3. Image copies

An image copy is a copy of a single file (datafile, archivelog, or
controlfile). It is very similar to an O/S copy of the file. It is not
a backupset or a backup piece. No compression is performed.

2.4. Full backup sets

A full backup is a backup of one or more datafiles that contains all used
blocks in the datafile. Blocks that have never been used are not backed up
i.e. oracle performs backup set compression.

2.5. Incremental backup sets

An incremental backup is a backup of one or more datafiles that contains
only those blocks that have been modified since a previous backup at the
same or lower level. As with full backups, compression is performed.

2.6. File multiplexing

Datablocks from multiple datafiles can be multiplexed in the same
backupset.

2.7. Recovery catalog resyncing

Resyncing the recovery catalog involves synchronising the recovery
catalog with the target database controlfile. Certain operations perform
this implicitly. To resync manually, issue the 'resync catalog;' command
from RMAN. The catalog should be resynced frequently, especially if
the target database generates many archive logs. It should also be
resynced after making any structural changes to the target database.
Although the target database's controlfile is automatically updated
whenever new controlfile records are created (for example, creation of
new archived logs or new datafiles), if the target is not resync'd
and a backup controlfile is restored, the new records must be cataloged
manually (catalog archivelog '';).

2.8. Snapshot Controlfile

When RMAN needs to resynchronize from a read-consistent version
of the control file, it creates a temporary snapshot control file. The default
name for the snapshot control file is port-specific. Use the 'set snapshot
controlfile name to file_name' command to change the name of the snapshot
control file; subsequent snapshot control files that RMAN creates use the
name specified in the command. The snapshot control file name can also
be set to a raw device. This operation is important for OPS databases in
which more than one instance in the cluster use RMAN because server sessions
on each node must be able to create a snaphost control file with the same name
and location.

2.9. Resetlogs Operation

Whenever you open the database with the RESETLOGS option, all datafiles
get a new RESETLOGS SCN and timestamp. Archived redo logs also have
these two values in their header. Because Oracle will not apply an archived
redo log to a datafile unless the RESETLOGS SCN and timestamps match,
the RESETLOGS operations prevents you from corrupting your datafiles with
old archived logs.

2.1.0 Database Incarnation

Whenever you perform incomplete recovery or perform recovery using a
backup control file, you must reset the online redo logs when you open the
database. The new version of the reset database is called a new incarnation.
All archived redo logs generated after the point of the RESETLOGS on the
old incarnation are invalid in the new incarnation.

2.1.1. Resetting the Recovery Catalog

Before you can use RMAN again with a target database that you have
opened with the RESETLOGS option, notify RMAN that you have reset
the database incarnation. The reset database command directs RMAN
to create a new database incarnation record in the recovery catalog.
This new incarnation record indicates the current incarnation. RMAN
associates all subsequent backups and log archiving done by the target
database with the new database incarnation. If you issue the ALTER
DATABASE OPEN RESETLOGS statement but do not reset the
database, then RMAN cannot access the recovery catalog because it
cannot distinguish between a RESETLOGS command and an accidental
restore of an old control file. By resetting the database, you inform
RMAN that the database has been opened with the RESETLOGS option.
In the rare situation in which you wish to undo the effects of opening
with the RESETLOGS option by restoring backups of a prior incarnation
of the database, use the 'reset database to incarnation key' command to
change the current incarnation to an older incarnation.
 

3. The recovery catalog

The recovery catalog is a repository of information that is used and
maintained by RMAN. RMAN uses the information in the recovery
catalog to determine how to execute requested backup and restore actions..'.

The recovery catalog can be in a schema of an existing Oracle8 database.
However if RMAN is being used to backup multiple databases, it is probably
worth creating a dedicated recovery catalog database. THE RECOVERY CATALOG
DATABASE CANNOT BE USED TO CATALOG BACKUPS OF ITSELF.

To set up the recovery catalog, firstly ensure that catalog and catproc
have been run, then execute the following:

    SVRMGR> spool create_rman.log
    SVRMGR> connect internal
    SVRMGR> create user rman identified by rman
    temporary tablespace temp
    default tablespace rcvcat quota unlimited on rcvcat;
    SVRMGR> grant recovery_catalog_owner to rman;
    SVRMGR> grant connect, resource to rman;
 

Note: Following steps only apply for an Oracle8 8.0.x catalog creation.

    SVRMGR> connect rman/rman
    SVRMGR> @?/rdbms/admin/catrman

Check create_rman.log for errors. The above commands assume that the
TEMP and RCVCAT tablespaces have been created.

In Oracle8i the catalog is created a little differently.

Note: Following steps only apply to Oracle8i 8.1.5 and greater.

From the UNIX shell run:

    % set ORACLE_SID=RCAT
    % rman catalog rman/rman
    RMAN> create catalog;

This will generate the recovery catalog schema in the default tablespace for
RMAN.

Also ensure that catproc has been run on the target database as SYS
(do _not_ use SYSTEM); RMAN makes extensive use of RPCs.

It is very important that the recovery catalog database is backed up
regularly and frequently.

Note: Although you are not required to use a recovery catalog with RMAN,
it is recommended. Because most of the information in the recovery catalog
is available via the target database's controlfile, RMAN can use this
information for recovery purposes.
 

4. Starting RMAN

RMAN has a command line interface, or can be run from Enterprise Manager.
For the purposes of this document, only the CLI will be covered.

The command line interface has following syntax:

    rman target [rcvcat | cmdfile< qstring> |
    msglog | append | trace ]

Argument     Quoted String Description

TARGET A connect string containing a userid and password for the
                database on which Recovery Manager is to operate.

                rman target system/manager@target

RCVCAT A connect string that contains a userid and password for the
                database that contains the recovery catalog.

                rman rcvcat rman/rman@rcvcat

CMDFILE The name of a file that contains the input commands for
                RMAN. If this argument is specified, RMAN operates in batch
                mode; otherwise, RMAN operates in interactive line mode.

MSGLOG The name of a file where RMAN records commands and output
                Results. If not specified, RMAN outputs to the screen.

APPEND This parameters causes the msglog file to be opened in append
                mode. If this parameter is not specified and a file with the
                same name as the msglog file already exists, it is overwritten.

TRACE     A file name where RMAN will dump a trace information.
                (useful feature for RMAN jobs debugging)
 
 

For the purposes of the following examples, assume that

    - the target database is called "targdb" and has the same TNS alias
    - "targdba" has been granted SYSDBA privileges
    - the recovery catalog database is called "rcat" and has the same TNS alias
    - the schema containing the recovery catalog is "rman" (same password)

Before invoking RMAN, set the NLS_DATE_FORMAT and NLS_LANG environment
variables. Much of the RMAN LIST output is date/time related. It is often
necessary to have this information displayed as accurately as possible
when performing time-based recovery. Example NLS settings:

    NLS_LANG=AMERICAN_AMERICA.WE8ISO8859P1
    NLS_DATE_FORMAT=DD-MON-YYYY HH24:MI:SS

For RMAN to connect to the recovery catalog and the target database, the
recovery catalog database must be OPEN, while the target instance must be
at least STARTED. If not, RMAN will give an error. To perform backups with
the target database open, the target MUST be in archivelog mode.

4.1. Connecting to RMAN without a recovery catalog

Set ORACLE_SID to be the target database, and issue the following:

    % rman nocatalog
    RMAN> connect target
    or if the target database uses a password file,
    RMAN> connect target targdba/@targdb

4.2. Connecting to RMAN with a recovery catalog

    % rman rcvcat rman/rman@rcat
    RMAN> connect target
    or if the target database uses a password file,
    % rman rcvcat rman/rman@rcat target targdba/@targdb
 

Note: Recovery Manager automatically requests a connection to the target
database as SYSDBA. In order to connect to the target database as SYSDBA,
you must either:

1. Be part of the operating system DBA group with respect to the
target database. This means that you have the ability to CONNECT
INTERNAL to the target database without a password.

-or -

2. Have a password file setup. This requires the use of the "orapwd"
command and the initialization parameter "remote_login_passwordfile".

Note: The connect string (for example, @targdb) should be a valid TNS
alias, as specified in the local to the rman utility tnsnames.ora file .
 

4.3. Using RMAN
 

Once connected to the target database, you can specify RMAN commands
either interactively or by using stored scripts. An example of
using RMAN interactively would be:

    RMAN> resync catalog;

An example of calling a stored script would be:

    RMAN> execute script alloc_1_disk;

To create/replace a stored script:

    RMAN> replace script alloc_1_disk {
    2> allocate channel d1 type disk;
    3> }
 

5. Register the target database

Database status:
Recovery catalog: open
Target: mounted or open

The target database must be registered with the recovery catalog before
using RMAN against the database for the first time:

    RMAN> register database;
 

6. Adding existing backups to the recovery catalog

Database status:
Recovery catalog: open
Target: mounted or open

If user-created backups existed under version 8.x prior to registering with
the target database, these can be added to the recovery catalog as follows:

    RMAN> catalog datafilecopy '/supp/ .... /systargdb.dbf';

To view this file in the catalog, use the following command:

    RMAN> list copy of database;
 

7. Backing up in noarchivelog mode

Database status:
Recovery catalog: open
Target: database mounted

Recovery catalog database is OPEN, target database is started (optionally
mounted). Because the target database is not in archivelog mode, it must
not be open when performing backups of datafiles. This would be equivalent
of making filesystem copies of datafiles without putting tablespaces into
hot backup mode. If the database is open and not in archivelog mode, RMAN
will generate an error when you attempt to perform a datafile backup

7.1. Example of how to back up a complete database

    RMAN> run {
    2> # backup the complete database to disk
    3> allocate channel dev1 type disk;
    4> backup
    5> full
    6> tag full_db_sunday_night
    7> format '/oracle/backups/db_t%t_s%s_p%p'
    8> (database);
    9> release channel dev1;
    10> }

Line#
2: Comment line (anything after the '#' is a comment)
3&9: See section 15 - Channels
5: Full backup (default if full or incremental not specified)
6: Meaningful string (<=30 chars)
7: Filename to use for backup pieces, including substitution variables.
8: Indicates all files including controlfiles are to be backed up

To view this backup in the catalog, use the following command:

    RMAN> list backupset of database;
 

7.2. Example of how to back up a tablespace

    RMAN> run {
    2> allocate channel dev1 type disk;
    3> backup
    4> tag tbs_users_read_only
    5> format '/oracle/backups/tbs_users_t%t_s%s'
    6> (tablespace users);
    7> release channel dev1;
    10> }

Line#
6: Specifying only the USERS tablespace for backup

To view this tablespace backup in the catalog, use the following command:

    RMAN> list backupset of tablespace users;

If for example the USERS tablespace is going to be put READ ONLY after
being backed up, subsequent full database backups would not need to
backup this tablespace. To cater for this, specify the 'skip readonly'
option in subsequent backups.

Note that although this is a tablespace backup, the target database
does NOT have to be open, only mounted. This is because tablespace
information is stored in the controlfile in o8.
 

7.3. Example of how to backup individual datafiles

    RMAN> run {
    2> allocate channel dev1 type 'SBT_TAPE';
    3> backup
    4> format '%d_%u'
    5> (datafile '/oracle/dbs/sysbigdb.dbf');
    6> release channel dev1;
    7> }

Line#
2: Allocates a tape drive using the media manager layer (MML)
Note that no tag was specified and is therefore null.

To view this tablespace backup in the catalog, use the following command:

    RMAN> list backupset of datafile 1;

7.4. Copying datafiles

    RMAN> run {
    2> allocate channel dev1 type 'SBT_TAPE';
    3> copy datafile '/oracle/dbs/temp.dbf' to '/oracle/backups/temp.dbf';
    4> release channel dev1;
    5> }

To view this file copy in the catalog, use the following command:

    RMAN> list copy of datafile '/oracle/dbs/temp.dbf';

Copying a datafile is different to backing up a datafile. A datafile copy
is an image copy of the file. A backup of the file creates a backupset.

7.5. Backing up the controlfile

    RMAN> run {
    2> allocate channel dev1 type 'SBT_TAPE';
    3> backup
    4> format 'cf_t%t_s%s_p%p'
    5> tag cf_monday_night
    6> (current controlfile);
    7> release channel dev1;
    8> }

Note that a database backup will automatically back up the controlfile.
 

8. Backing up in archivelog mode

Database status:
Recovery catalog: open
Target: instance started, database mounted or open

The commands are identical to those in section 7 except that the target
database is in archivelog mode.

8.1. Backing up archived logs

The following script backs up all archive logs:

    RMAN> run {
    2> allocate channel dev1 type disk;
    3> backup
    4> format '/oracle/backups/log_t%t_s%s_p%p'
    5> (archivelog all);
    6> release channel dev1;
    7> }

The following script backs up archive logs from sequence# 90 to 100:

    RMAN> run {
    2> allocate channel dev1 type disk;
    3> backup
    4> format '/oracle/backups/log_t%t_s%s_p%p'
    5> (archivelog from logseq=90 until logseq=100 thread 1);
    6> release channel dev1;
    7> }

The following script backs up all archive logs generated in the past
24 hours. Furthermore it actually deletes the logs after backing them
up. If the backup fails, logs will NOT be deleted:

    RMAN> run {
    2> allocate channel dev1 type disk;
    3> backup
    4> format '/oracle/backups/log_t%t_s%s_p%p'
    5> (archivelog from time 'sysdate-1' all delete input);
    6> release channel dev1;
    7> }

To view the archive logs in the catalog, use the following command:

    RMAN> list backupset of archivelog all;

Note that RMAN will backup specified logs if it finds them. If it can't
find a log, it will report rman-6089 error:
"archived log %s not found or out of sync with catalog",
and it will abort a backup session.
 

8.2. Backing up the online logs

Online logs CANNOT be backed up using RMAN; they must be archived first.
To do this, you can issue SQL commands from RMAN e.g.

    RMAN> run {
    2> allocate channel dev1 type disk;
    3> sql "alter system archive log current";
    4> backup
    5> format '/oracle/backups/log_t%t_s%s_p%p'
    6> (archivelog from time 'sysdate-1' all delete input);
    7> release channel dev1;
    8> }

The above script might be run after performing a full 'database open'
backup. It would ensure that all redo to recover the database to a
consistent state would be backed up.

Note, you cannot tag archive log backupsets.
 

9. Incremental backups

A level N incremental backup backs up blocks that have changed since the
most recent incremental backup at level N or less.

9.1. Level 0 - the basis of the incremental backup strategy

    RMAN> run {
    2> allocate channel dev1 type disk;
    3> backup
    4> incremental level 0
    5> filesperset 4
    6> format '/oracle/backups/sunday_level0_%t'
    7> (database);
    8> release channel dev1;
    9> }

Line#
4: Level 0 backup - backups of level > 0 can be applied to this
5: Specifies maximum files in the backupset

A list of the database backupsets will show the above backup. The 'type'
column is marked 'Incremental'; the 'LV' column shows '0'.

9.2. Example backup strategy using incremental backups

A typical incremental backup cycle would be as follows:

    - Sun night - level 0 backup performed
    - Mon night - level 2 backup performed
    - Tue night - level 2 backup performed
    - Wed night - level 2 backup performed
    - Thu night - level 1 backup performed
    - Fri night - level 2 backup performed
    - Sat night - level 2 backup performed

If the database suffered a failure on Sat morning and this resulted in
a restore operation, RMAN could recover to the point of failure by
restoring the backups from Sunday, Thursday, and Friday. This is
because Thursdays level 1 backup contains all changes since Sunday, and
Friday's level 2 backup contains all changes since Thursday. Whether
the database could be completely recovered would depend on whether
archive logging is enabled.
 

10. Cumulative incremental backups

A cumulative incremental backup backs up all blocks that have changed since
the the most recent incremental backup at level N-1 or less (contrast with
non-cumulative incremental backups that backup blocks that have changed
since the the most recent incremental backup at level N or less). This
means that more work is done in performing the backup (duplication of
backup effort), but time may be saved when restoring (potentially fewer
backupsets to restore).

    RMAN> run {
    2> allocate channel dev01 type disk;
    3> backup incremental level 1 cumulative database;
    4> release channel dev01;
    5> }
 
 

11. Checking backup progress

To check the backup progress run the following sql against the target
database:

select sid, serial#, context
          round(sofar/totalwork*100,2) "% Complete",
         substr(to_char(sysdate,'yymmdd hh24: mi:ss'),1,15) "Time Now"
from  v$session_longops
where compnam = 'dbms_backup_restore';  -- for 8.0
where substr(opname,1,4) = 'RMAN';          -- for 8.1

This will produce an output such as:

SID         SERIAL#    CONTEXT    % Complete            Time Now
---------- ----------    ----------       -----------------      ---------------
12                                                     56                           980408 14:21:07
 
 

12. Recovery

As with backup, recovery is probably best explained with a few examples

12.1. Database open, datafile deleted

Datafile has been deleted from a running database. There are two methods
of open database recovery: restore the datafile and recover either the
datafile, or the tablespace. The next two examples show both methods:

(a) Datafile recovery

    RMAN> run {
    2> allocate channel dev1 type disk;
    3> sql "alter tablespace users offline immediate";
    4> restore datafile 4;
    5> recover datafile 4;
    6> sql "alter tablespace users online";
    7> release channel dev1;
    8> }

(b) Tablespace recovery

    RMAN> run {
    2> allocate channel dev1 type disk;
    3> sql "alter tablespace users offline immediate";
    4> restore tablespace users;
    5> recover tablespace users;
    6> sql "alter tablespace users online";
    7> release channel dev1;
    8> }

Note that if it is the system tablespace datafiles to be restored, the
database must be closed. It is not possible to offline the system
tablespace.

12.2. Complete restore (lost online redo) and rollforward - database closed

    RMAN> run {
    2> allocate channel dev1 type disk;
    3> set until logseq=105 thread=1;
    4> restore controlfile to '/oracle/dbs/ctrltargdb.ctl';
    5> replicate controlfile from '/oracle/dbs/ctrltargdb.ctl';
    6> restore database;
    7> sql "alter database mount";
    8> recover database;
    9> sql "alter database open resetlogs";
    10> release channel dev1;
    11> }
    RMAN> reset database;
Notes:
- The 'set until' command dictates at which log sequence recovery will
stop. It is critical that this command is issued BEFORE datafiles
are restored, otherwise RMAN will attempt to restore the most recent
set of datafiles, which could be ahead of the specified log
- The 'replicate controlfile' copies the restored controlfile to
the controlfiles referenced in init.ora
- Because the database is opened with resetlogs, it is necessary to
register the new incarnation of the database with the RESET DATABASE
command. As with v7, it is important to take a full backup of the
database immediately after a resetlogs

12.3. Restore of a subset of datafiles, complete recovery

    RMAN> run {
    2> allocate channel dev1 type disk;
    3> sql "alter database mount";
    4> restore datafile 2;
    5> restore datafile 3;
    6> restore archivelog all;
    7> recover database;
    8> sql "alter database open";
    9> release channel dev1;
    10> }
 

13. Scripts

It is very easy to create and replace stored scripts with RMAN. E.g.

    RMAN> create script alloc_disk {
    2> # Allocates one disk
    3> allocate channel dev1 type disk;
    4> setlimit channel dev1 kbytes 2097150 maxopenfiles 32 readrate 200;
    5> }

    RMAN> replace script rel_disk {
    2> # releases disk
    3> release channel dev1;
    5> }

    RMAN> replace script backup_db_full {
    2> # Performs a complete backup
    3> execute script alloc_disk;
    4> backup
    5> .....
    6> execute script rel_disk;
    7> }

The first 2 scripts allocate and deallocate channels respectively. The
alloc_disk script additionally specifies the maximum size of backup
pieces created on this channel (kbytes), the maximum number of input files
that a backup will have open (maxopenfiles), and the maximum number of
buffers per second which will be read from each of the input datafiles.

The 3rd script calls the previously stored scripts either side of
performing a backup.

Example of executing a stored script:

    RMAN> run {
    2> execute script backup_db_full;
    3> }

Note that a stored scripts must be called from within a job command
list i.e. run { .... execute

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