backup strategy for oracle database

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Backup Strategy for Oracle

February 2008 4

Contents

Int roducti on ....................................................................................................... 5

Example 1 ...................... ..................... ..................... ...................... .................... 6

Example 2 ...................... ..................... ..................... ...................... .................... 8

Example 3 ...................... ..................... ..................... ...................... .................... 9

Summary.......................................................................................................... 10

Add it ional Info rmat ion ..................................................................................... 11

SAP Lib rary ...................................................................................................................... 11

SAP Notes ........................................................................................................................ 11




February 2008 5

Introduction

SAP data is stored in a relational database. A data backup consists of database files and SAP filessuch as programs, log files, and so on, which are stored centrally under /usr/sap/... . You use

operating system tools to back up this directory tree, which is part of the hierarchical file system. Asthis data generally only changes when profile parameters are modified or after an upgrade, you onlyneed to perform a backup in such cases. However, for database objects the situation is completelydifferent, as we describe in this document.

Since it is generally very dynamic, SAP data requires a comprehensive security strategy. Thefollowing examples illustrate two appropriate and one faulty backup strategy. In the event of an error,the faulty strategy results in the complete loss of all business data.

In the examples below the tape administration is controlled by BRBACKUP and BRARCHIVE.Nevertheless, the strategies shown in the examples below are valid for other backup strategies suchas BACKINT or RMAN.




February 2008 6

Example 1The size of the database is less than 100 GB and daily backups are possible.

As the SAP System does not have to be available after 18:00, you can perform the backup offline.

Alternatively, you can perform the backup at a time when the transaction load is low. A full backup ofthe data (without log redo information) fits onto two tapes, if DLT techniques are used.

Backup Strategy with Daily Complete Backups

Number of tapesfor database data

days

2

1

S M T W T F SS M T

locked: retention period = 28 days

Key:

Number of tapesfor redo logs

2

1


total: (52+x) tapes

3

free locked

Tape re-use possible


W T F S SM T W T F SS M TW T F S S

total: (56+x) tapes

daysS M T W T F SS M TW T F S SM T W T F SS M TW T F S S

To be able to deal with a faulty backup, several generations of backups have to be available.Therefore, for this example, the retention period is set to 28 days and consequently 27 backupgenerations are available in the event of database failure. The tape pool ought to contain severalreserve tapes, shown as “+ x” in the above graphic. The additional tapes – we recommendapproximately 30% of the required number – are intended as a reserve in case the amount of data tobe backed up greatly increases or an extra unplanned backup becomes necessary.

Using a separate tape pool, you also need to back up the redo log information generated during theday, which is temporarily stored on a separate large disk until the tape backup. As this data is

necessary to recover a database after restoring a data backup, never set the retention period for theredo log tapes to less than the retention period for the data backup tapes. Particularly in the case of anonline backup, it is best to always back up redo logs directly after the data backup.

Without redo log information the online backup is worthless.

As the redo log information is much more dynamic than the database data, even more reserve tapesare required.

We recommend you to back up the redo logs twice for extra security, so that you need 2 x (52 + x)tapes in the redo log tape pool.

The number of tapes required depends on the hardware implemented and the tape capacity available,

as shown in the table below:




February 2008 7

Capacity and Performance of Tape devices

Type Capacity (GB) Transfer Rate (GB / hour)

IBM 3590/Magstar 20 - 40 10 - 15

DLT 7000 35 – 70 15 – 20

DST 310 / 312 50 30 - 50




February 2008 8

Example 2

The database is too large for a complete daily offline or online backup and has to be available 24hours a day on 5 working days.

Therefore, an online backup is chosen and spread over two days, part A and part B. It runs during thenight, as this is the only time when the transaction load is low.

Backup Strategy for a Very Large Database with Partial Backups (A) and (B)

Numberof tapesfordatabasedata

days

4

total:(40+x) tapes

Numberof tapesfor redo

logs

days

2

1

total:(19+x) tapes

3

8


AA BB AA BB AA BB

AA

BB

++

AA BB


WeSo Mo Tu We Th Fr Sa So Mo Tu



Key: free locked

WeSo Mo Tu We Th Fr Sa So Mo Tu

This strategy is generally subject to more errors than the one described above in the first examplebecause the database administrator is responsible for the correct distribution of the data to the partialbackups (A) and (B). Furthermore, the risk of losing data is greater because online backups are onlyconsistent in combination with redo information.

Here, the number of tapes required for the data backup is 40 + x. For security reasons, an additionalfull offline backup is performed at the weekend. If this strategy is used with a retention period of 7

days, only 4 generations of backups will be available.

The redo log files are even more important than in the first example, as the onlinebackups are absolutely worthless without them. Here it is essential to back up the redodata twice.




February 2008 9

Example 3

As in the first example, a full backup is performed offline once a day. The retention period is set to 1day so the two tapes required are overwritten each day.

In the event of a disk error, this single backup has to be used. If it cannot be read, the database isdestroyed. As the redo information has also not been saved separately, in the case of a disk failurewhich affects data and redo information, all transactions executed since the last backup will be lost.

Do not follow this example. It is included to illustrate a faulty backup approach.

Faulty Security Strategy

Numberof tapes

fordatabase

data

days

2

total:2 tapes

Numberof tapesfor redologs

days

2

1

Sa So Mo Tu We Th Fr Sa So Mo Tu

Danger: possible loss of daily transactions

4 Danger: possible loss of all data

Tapes only locked briefly because retention period = 1 day

No backup of redo information

Tapes re-used each day

Sa So Mo Tu We Th Fr Sa So Mo Tu

Key: free locked




February 2008 10

Summary

The strategy described in the first two examples, or any similar strategy based on the same principles,enables you to recover the database to any point in time (that is, you can eliminate application errors,also called logical errors). Without the redo information, an offline backup only enables the state of thedatabase at the time of the last backup to be recovered. An online backup without redo information isworthless.

The different situations described above only represent simplified examples intended to illustrate theproblems involved.

SAP recommends the following for your backup strategy:

• A retention period of at least 14 days, preferably 28 or 30 days

• 30 % reserve tapes in the tape pool

• Backup of the redo log information (that is, the archive log files) directly after eachdatabase backup and creation of a second copy of archive log files

• A minimum of 10 generations of complete database backups




February 2008 11

Additional Information

SAP Library

You can find more information on Oracle database administration and the contents of this document inthe SAP Library as follows:

All paths refer to Release SAP NetWeaver Process Integration 7.1 of the SAP Library.

1. Call up the SAP Help Portal at help.sap.com/nwpi71 → KNOWLEDGE CENTER FOR SAP

NETWEAVER PROCESS INTEGRATION 7.1 → SAP NetWeaver Process Integration Library English .

2. Choose Administrator’s Guide → Technical Operations for SAP NetWeaver → Administration of

Databases → Database Administration for Oracle .

3. Choose one of the following:o SAP Database Guide: Oracle

Choose one of the following:

• Approach to Oracle DBA → Database Backup or Restore and Recovery

• BR*Tools for Oracle DBA → BR*Tools in Action → Backup and Database Copy with BR*Tools

• BR*Tools for Oracle DBA → BR*Tools in Detail → BRBACKUP or BRARCHIVE or BRRESTORE or BRRECOVER

o CCMS: Oracle

You can also find these plus selected extracts from the SAP Library at:

www.sdn.sap.com/irj/sdn/ora → SAP on Oracle Knowledge Center → SAPDocumentation in Help Portal

SAP Notes

You can find SAP Notes at:

service.sap.com/notes

backup strategy for oracle database

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