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Re: Oracle8i (8.1.6) Backup and Recovery Questions

From: Sybrand Bakker <oradba_at_sybrandb.demon.nl>
Date: Thu, 13 Dec 2001 19:13:26 +0100
Message-ID: <blrh1uscj12h2hunlcrovcjrelqqr67nrt@4ax.com>


On Thu, 13 Dec 2001 16:30:16 GMT, "Alex Stankevich" <alex.stankevich_at_redshift-tech.com> wrote:

>I have questions about restoring an oracle db from a hot backup.
>
>Here is the scenario that I am experimenting with and the recovery
>actions I'm taking:
>
>All the disks on my server machine are fried and all data is lost. I
>need to restore the machine and Oracle.
>
>I do a weekly cold backup of Oracle running in ARCHIVELOG mode. In
>addition I do a daily hot backup of Oracle.
>
>Restoration procedure:
>
>1. I restore the machine by first restoring a low level disk image of
>the machine just before it went to production (with Oracle already
>installed and setup).
>
>2. Then I restore Oracle to its last cold backup state. I take the
>latest cold backup of oracle and restore all of its files: control
>files, data files and online redo files.
>
>3. Then I delete all the online redo logs.
>
>4. I restore the backed up data files and archived redo logs
>taken during the last hot backup.
>
>5. Then I perform incomplete media recovery
>
> SVRMGRL> connect internal;
> SVRMGRL> startup mount;
> SVRMGRL> recover database until cancel using backup control file;
>
>...hitting enter until I get to the prompt for the last redo archive, then I
>hit cancel.
>
> SVRMGRL> alter database open resetlogs;
>
>6. I do a cold backup of the db.
>
>
>Q1: I was able to run "recover database until cancel using backup
>control file;" without actually restoring the backed up version of the
>control file. Should I have restored the backed up control file into
>the oradata/<db-name> directory prior to running step 5?
>
>Q2: Why did the recovery work even though I didn't restore the hot
>backed up version of the control file? Doesn't the control file
>restored from the cold backup have an old SCN?
>
>Q3: How would Oracle know about the necessity to apply archived redo
>logs? (Is it from detecting data files that have newer SCNs than that
>in the control file?)
>
>
>Thanks,
>Alex.
>

3 You shouldn't have made a backup of the online redo logs in the first place

Q1 That would have made the database consistent, so it would have refused to recover anything.

Q2 you indicated the controlfile came from a backup. Hence, recovery doesn't rely on the information the controlfile. You are conducting incomplete recovery as opposed to complete recovery. In the latter case you would have forced the database into recovery by restoring the most recent copy of the controlfile.

Q3 Yes

Please check out the books section of Howard Rogers site www.hrjdba.com

Hth

Sybrand Bakker, Senior Oracle DBA

To reply remove -verwijderdit from my e-mail address Received on Thu Dec 13 2001 - 12:13:26 CST

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