rman

RMAN & SMR (Server-Managed Recovery)

Posted by Narashim Reddy .R on August 18, 2009

1 Votes

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 ‗<logname>‘;).

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 <qstring> [rcvcat <qstring> | cmdfile <qstring> |

msglog <qstring> | append | trace <qstring>]

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/<password>@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/<password>@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:


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:


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 {


3> backup

4> tag tbs_users_read_only

5> format ‗/oracle/backups/tbs_users_t%t_s%s‘

6> (tablespace users);


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‘);


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 {


3> copy datafile ‗/oracle/dbs/temp.dbf‘ to ‗/oracle/backups/temp.dbf‘;


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 {


3> backup

4> format ‗cf_t%t_s%s_p%p‘

5> tag cf_monday_night

6> (current controlfile);


8> }

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

8. Backing up in archivelog mode

Database status:


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 {


3> backup

4> format ‗/oracle/backups/log_t%t_s%s_p%p‘

5> (archivelog all);


7> }

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

RMAN> run {


3> backup


5> (archivelog from logseq=90 until logseq=100 thread 1);


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 {


3> backup


5> (archivelog from time ‗sysdate-1′ all delete input);


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 {


3> sql ―alter system archive log current‖;

4> backup


6> (archivelog from time ‗sysdate-1′ all delete input);


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 {


3> backup

4> incremental level 0

5> filesperset 4

6> format ‗/oracle/backups/sunday_level0_%t‘

7> (database);


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 {


3> backup incremental level 1 cumulative database;


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 {


3> sql ―alter tablespace users offline immediate‖;

4> restore datafile 4;

5> recover datafile 4;

6> sql ―alter tablespace users online‖;


8> }

(b) Tablespace recovery

RMAN> run {


3> sql ―alter tablespace users offline immediate‖;

4> restore tablespace users;

5> recover tablespace users;

6> sql ―alter tablespace users online‖;


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 {


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‖;


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 {


3> sql ―alter database mount‖;



6> restore archivelog all;

7> recover database;

8> sql ―alter database open‖;


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


4> setlimit channel dev1 kbytes 2097150 maxopenfiles 32 readrate 200;

5> }

RMAN> replace script rel_disk {

2> # releases disk


5> }

RMAN> replace script backup_db_full {

2> # Performs a complete backup

3> execute script alloc_disk;

4> backup

5> …..<backup commands here>

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 <script>; ….}.

It is possible to create a job command list in a flat file and call that

script from the O/S command line as an RMAN option. E.g. to call scripts

stored in a file called ‗weekly_cold_backup‘:

% rman <other RMAN options> cmdfile weekly_cold_backup

14. Parallelization

RMAN can parallelize it‘s operations. When creating backup sets, the

granule of parallelization is the backup set. E.g. if your backup consists

of 10 backup sets, RMAN will potentially use 10 channels. To create an

environment for this to take place, you must allocate sufficient channels

and dictate the number of backup sets created (using the filesperset

parameter). E.g. if you are backing up a database consisting of 50

datafiles and you allocate 20 channels and specify ‗filesperset 10′,

only 5 channels will be used. This is because only 5 backup sets (50/10)

will be created.

It is also possible to parallelize datafile copy backups by allocating

multiple channels, and specifying multiple datafiles in one copy command.

15. Corruption detection

SMR will back up datafiles that contain corrupt blocks. However it is

possible to set a limit on the number of datablock corruptions; if this

limit is exceeded the backup terminates. The limit is set using the

‗set maxcorrupt‘ clause.

E.g.

RMAN> replace script backup_db_full {

2> # Performs a complete backup

3> execute script alloc_disk;

4> set maxcorrupt for datafile 1 to 0;

5> backup

6> …..<backup commands here>

7> execute script rel_disk;

8> }

When the above script the backup will fail if ANY corrupt blocks are

found in datafile 1.

Block corruptions are detected by checksum mismatches during backups. The

checksum option is enabled by default but can be disabled by specifying

the ‗nochecksum‘ option.

16. Channels

A channel is a connection from RMAN to a target database. The ‗allocate

channel‘ command starts a server process on the target instance. It also

specifies the type of I/O device that the server process will use to

perform the backup or restore operation.

Channel control commands can be used to:

- Control the O/S resources RMAN uses

- Affect the degree of parallelism (see section 13)

- Specify limits on I/O bandwidth (set limit read rate)

- Specify limits on the size of backup pieces (set limit kbytes)

- Specify limits on the number of concurrently open files (set limit

maxopenfiles)

17. Report & list commands

17.1. List

The list command queries the recovery catalog to produce a formatted

listing of contents. E.g.

RMAN> list backupset of datafile 1;

Output:

Key File Type LV Completion_time Ckp SCN Ckp Time

——- —- ———— — ————— ———- ——–

165 1 Full Oct 03 11:24 32022 Oct 03 11:24

208 1 Full Oct 24 14:27 52059 Oct 24 14:26

219 1 Full Oct 24 14:31 52061 Oct 24 14:31

<< other entries here >

RMAN> list backupset of archivelog all;

Output:

Key Thrd Seq Completion time

——- —- ——- —————

179 1 94 Oct 03 11:26

179 1 95 Oct 03 11:26

<< other entries here >

17.2. Report

The report command also queries the recovery catalog, However, the report

command syntax is constructed in such a way to produce a more useful

listing. E.g. the following command can be used to list all datafiles

in a database that have had UNRECOVERABLE operations performed on objects

in those datafiles since the last backup:

RMAN> report unrecoverable database;

18. Hints, tips, & best practices

18.1. Resyncing the recovery catalog

It is very important that the recovery catalog be as up to date as

possible i.e. it should reflect the state of the target database. This

is achieved by resyncing the catalog from the target controlfile.

There are two types of resync operation: full and partial. Furthermore

a resync can be explicit or implicit.

A full resync updates the catalog with ALL controlfile information that

has changed since the last resync. This includes changes to the physical

structure of the database. A manual (explicit) resync performs a full

resync, whilst full (implicit) resyncs are performed after an SMR backup.

A partial resync only updates the catalog with redo log, backupset, and

datafile copy information i.e. physical structure changes are NOT

refreshed. A partial (implicit) resync is performed before an SMR backup.

At a MINIMUM, you should resync the recovery catalog at intervals less

than the init.ora parameter CONTROL_FILE_RECORD_KEEP_TIME. After this

number of days, controlfile information will be overwritten. Because

resyncing is a relatively cheap operation, it is advisable to resync

as often as possible, especially if the database switches logs

frequently. The following sample shell script could be scheduled to

run hourly:

rman target un/pw@<target alias> rcvcat un/pw@<rcvcat alias> << EOF

resync catalog;

exit;

EOF

18.2. Deleting archive logs

As can be seen from an earlier example, it is possible to direct an SMR

server session to delete archived redo logs once they have been backed

up. This option should obviously be used with extreme caution! Only

ever delete archivelogs if you are 100% satisfied that you have good

copies/backups elsewhere.

18.3. Keep it simple

As with all backup & recovery strategies, they should be as simple as

possible, and should be tested thoroughly.

A few simple stored scripts should be adequate for the vast majority

of backup & recovery requirements.

18.4. RMAN errors

When RMAN goes wrong it‘s spectacular! The error stacks are usually

very long. If an error is reported, it is worth getting the complete

stack sent to support as most of the errors will not help in diagnosing

the problem.

19. Limitations

19.1 Enterprise Edition

Only the following features are available with the Enterprise Edition software:

Multiple Channels

Incremental Backups

Duplexed Backups

rman

Documents

backup controlfile

incremental backup

previous backup

backup set compression

backup piece size

backup initialization

number of backup pieces

complete set of backup