Advanced Databases 1

DBA: Backups

Advanced Databases 2

Agenda

• Define backup• Discuss Backup Terminology• Explain various backup and restore

options in Oracle• Demonstrate backups in Oracle

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Question: What is a Backup?

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Backup

A procedure for making extra copies of data for the purpose of

restoration in case of loss or damage.

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Backup Terminology

• Hot Backup• Cold Backup

• Full Backup • Incremental Backup• Differential Backup

• Backup Window• Backup Job

• On-line• Off-line• Off-Site

• Data Compression• Data Deduplication• Data Encryption

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Types of Backup

• A full backup (level 0) is a complete copy of a partition.

• An incremental backup (level 1) is an archive of only the files that have changed since the last full backup.

• A differential backup (level 2, 3, etc) is an archive of only the file that have changed since the last backup (not necessarily full backup.

Backup Sun (F) Mon Tue Wed Thu Fri Sat

Full 2TB 2TB 2TB 2TB 2TB 2TB 2TB

Incr. 2TB 1GB 1.2GB 1.6GB 1.9GB 2.3GB 2.8GB

Diff 2TB 1GB 0.2GB 0.4GB 0.3GB 0.4GB 0.5GB

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Short-Sighted Backups – Why?

• Why are each of these a bad backup strategy? Advantages / Disadvantages?

Only taking Cold, Full BackupsOne Full Offsite backup Just hot backupsFull backups monthly, differentials

daily.

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Let’s Talk Strategy

• Ideally we’d like to backup everything all the time and keep it around forever.

• Realistically, we cannot do that.• You need a combination of short-term

and long-term strategies. For example:– At least 3 copies of the data, 1 off site.– Hot backups for convince, cold backups for

insurance D/R.– Test your restore process, at multiple levels.– Others?

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Database Backup and Recovery

• Important database administration support tasks include:– Backup• Offline/cold• Online/hot

– Recovery• Restore Entire tablespaces• Build test / dev environments from restores• Recover missing / erroneous data in tables.

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Creating Offline (Cold) Backups

1. Shut down database instance2. Copy specific database files to

alternate disk location1. Parameter file2. Control files3. Datafiles4. Not redo logs

3. Restart database instance

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Creating Online (Hot) Backups

1. Place database instance in ARCHIVELOG mode

2. Back up control file3. Back up datafiles4. Instruct database to write current

contents of redo log files to archive files- Create backup copies of archive log files

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Database Recovery

• Process of restoring database from either cold or hot backup files

• Necessary after database failure• Cold backup recovery:– Shut down database– Restore backed up control file and

datafiles to database server– Restart database

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Database Recovery (continued)

• Hot backup recovery:– Recover database to point at which last

hot backup created– Use control trace file to generate new

copy of control file– Restore backup copies of datafiles– Perform media recovery

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Demo – Start and Stop Oracle

• Let’s use OEM to start and stop your Oracle instance, then create a cold backup

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Oracle Backup Strategies

• Cold backups– Simplest to perform– Satisfactory for databases whose:

• Contents do not change very much • Users can tolerate downtime while DBA creates cold

backup files

• Hot backups – Complex to perform– Better suited for dynamic, mission-critical

databases

• If you setup a clustered environment you can perform cold backups without loss of service.

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Questions