| What files to restore? [message #51736] |
Tue, 11 June 2002 06:35  |
Michael
Messages: 61
Registered: October 1999
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Member |
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I'm searching for simple informations about restoring a complete oracle8-db.
In my cold-backup (NOARCHIVELOG-Mode) are included the data-files, the online-redo-logs and the controlfile (only OS-files).
What files I have to restore? And what following steps I have to do, before I can open this older version of the db?
It would be very nice if you could tell me additionally what files to restore and to do if the db is in ARCHIVELOG-Mode?
Thanks for all answers,
Michael.
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| Re: What files to restore? [message #51750 is a reply to message #51736] |
Tue, 11 June 2002 19:45  |
Vikas Gupta
Messages: 115
Registered: February 2002
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Senior Member |
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Hello Michael,
If you want to restore the whole DB then
you must restore all the datafiles, log files,
control files, parameter files to the original
locations.
In ArchieveLog Mode
If you are restoring after a crash, you can restore only the corrupted file, and start the recovery.
There is no need to restore all files.
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| Re: What files to restore? [message #51753 is a reply to message #51736] |
Wed, 12 June 2002 01:16 |
Michael
Messages: 61
Registered: October 1999
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Member |
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First of all, thanks for your reply, Vikas!
That means, if i want to restore the whole db (in NOARCHIVELOG-Mode) with my cold-backup, i have to restore following files: all datas, all ONLINE REDO LOGS, the control-files (i don't have created it with the BACKUP CONTROLFILE...Statement -> it's only an OS-File!).
If i have done this, can I start the DB without any further steps?
I had a look into the "Oracle Backup & Recovery Guide" and found following informations in chapter "Recovering a Database in NOARCHIVELOG Mode":
- Restore Datafiles
- Restore Controlfiles
-> ALTER DATABASE RECOVER DATABASE UNTIL CANCEL;
-> ALTER DATABASE OPEN RESETLOGS
Do you know, why Oracle don't recommend to restore the ONLINE-REDO-LOG-Files from a cold-backup?
I suppose, that I am going to loose modified data, which is stored in the online-redos, don't I???
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| Re: What files to restore? [message #51755 is a reply to message #51736] |
Wed, 12 June 2002 03:34 |
Vikas Gupta
Messages: 115
Registered: February 2002
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Senior Member |
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When Oracle says that, it means You are recovering from a crash, while I said only Restoring the database not recovering.
When ever a transaction takes place in Oracle, it is written in the Log Files. So when you recover from a crash.. Oracle will read from the log files to bring the database current. Thats why you don't restore back the logfiles during RECOVERY.
However in NOARCHIEVELOG mode, there is a good chance that you loose data. The Log files can be overwritten after all LogFiles are used.
Ex. you have 3 LogFiles, Log A, Log B and Log C, Oracle will write to LogA then to LogB then to LogC and again Back to LogA.
So if a crash occurs after LogA is written the second time, you may not be able to recover the data. While running in NOARCHIEVELOG mode, the ideal would be to size the redologs so that they are not over-written during the entire day. Then you take backup at night. That way there is very less chance that you loose data.
In ARCHIVELOG mode, the ARCH background process copies the redolog file to a different location before overwriting the data, hence no chance of data loss.
If you need further clarifications, please let me know.
Vikas.
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