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Assistance with recovering a database? [message #298616] Wed, 06 February 2008 17:17 Go to next message
bluca
Messages: 4
Registered: February 2008
Junior Member
I have an Oracle 9i database that we backup using EMC BCVs (mirror splits). We put the database into backup mode by running:
alter tablespace TABLE_SPACE_NAME begin backup;
for each tablespace on the system. Once that is complete, we split the BCV mirror and then put the database back to normal with:
alter tablespace TABLE_SPACE_NAME end backup;

The problem I have is that I've now got to recover the database, but we didn't realize we weren't backing up the archive and redo logs. I don't care if I lose the latest transactions because we can recreate a few days of data if necessary, but I can't afford to lose the historical data that is in this database. We have around 4Tb of historical data (hence using BCVs). Is it possible to recover the database without the archive logs?
Re: Assistance with recovering a database? [message #298617 is a reply to message #298616] Wed, 06 February 2008 17:26 Go to previous messageGo to next message
BlackSwan
Messages: 25045
Registered: January 2009
Location: SoCal
Senior Member
>Is it possible to recover the database without the archive logs?
NO!

You can restore to a point in time for the latest hotbackup or latest archived redo log file (which ever is more recent).
One should never backup active redo log files or control files.

P.S.
"backups" are only as good as the documented & tested recovery procedures.

[Updated on: Wed, 06 February 2008 17:29] by Moderator

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Re: Assistance with recovering a database? [message #298618 is a reply to message #298617] Wed, 06 February 2008 17:29 Go to previous messageGo to next message
bluca
Messages: 4
Registered: February 2008
Junior Member
anacedent wrote on Wed, 06 February 2008 17:26
>Is it possible to recover the database without the archive logs?
NO!
One should never backup active redo log files or control files.


So, I'm dead in the water without the archive logs? Sorry, I'm not a DBA. I'm a UNIX admin without access to any DBAs. Sad

What exactly does Oracle do to the data files and the existing data once you put it in online backup mode? It sounds pretty scary that losing the archive logs for current transactions means you can't get back any of your data.
Re: Assistance with recovering a database? [message #298619 is a reply to message #298616] Wed, 06 February 2008 17:36 Go to previous messageGo to next message
BlackSwan
Messages: 25045
Registered: January 2009
Location: SoCal
Senior Member
When was the most recent "hotbackup"?
Since the most recent hot backup, which archived redo file do you have?

In normal operation, the redo log files only get "change vectors".

>What exactly does Oracle do to the data files and the existing data once you put it in online backup mode?
In general terms when a tablespace is placed into "backup" mode,
when a block gets changed, the whole block is written to the redo file.

>It sounds pretty scary that losing the archive logs for current transactions means you can't get back any of your data.

How is Oracle to "know" what has changed since last hot backup?
The knowledge of what changed is contained in the redo files.
The information in these log files allow Oracle to REDO changes.
Re: Assistance with recovering a database? [message #298621 is a reply to message #298619] Wed, 06 February 2008 18:47 Go to previous messageGo to next message
bluca
Messages: 4
Registered: February 2008
Junior Member
anacedent wrote on Wed, 06 February 2008 17:36
When was the most recent "hotbackup"?
Since the most recent hot backup, which archived redo file do you have?

In normal operation, the redo log files only get "change vectors".

>What exactly does Oracle do to the data files and the existing data once you put it in online backup mode?
In general terms when a tablespace is placed into "backup" mode,
when a block gets changed, the whole block is written to the redo file.

>It sounds pretty scary that losing the archive logs for current transactions means you can't get back any of your data.

How is Oracle to "know" what has changed since last hot backup?
The knowledge of what changed is contained in the redo files.
The information in these log files allow Oracle to REDO changes.




right, i understand that. i just mean that older data has already been committed to the data files and i don't really care to redo any of the more recent changes. while we will certainly fix our backup process in the near future, we are currently stuck without proper backups of the archive logs.

so, is that it? without archive logs, a backup of all of the other files is just a waste of tape? i guess i'm at the point where i have to go to my management and explain that the data that we have on tape is completely unrecoverable.
Re: Assistance with recovering a database? [message #298622 is a reply to message #298616] Wed, 06 February 2008 19:00 Go to previous messageGo to next message
BlackSwan
Messages: 25045
Registered: January 2009
Location: SoCal
Senior Member
1) switch (redo) log file
2) start "hotbackup" of tablespaces
3) after all tablespaces have been snapshotted, switch (redo) log file
4) copy all archived redo log files generated between #1 & #4; inclusive.

With these files on tape you will be able to recover until #3.

If you desire to be able to recover to a point in time after #3,
you'll require the archived redo log files between #3 & when you wish to complete a PITR.

IMO, you should create a small test instance & practice DB recovery while documenting the steps required to succeed.
Re: Assistance with recovering a database? [message #298628 is a reply to message #298622] Wed, 06 February 2008 20:04 Go to previous messageGo to next message
bluca
Messages: 4
Registered: February 2008
Junior Member
is there anyone else out there other than anacedent who might be able to understand my question? just to clarify, i am NOT asking how to do proper backups. i am asking if there is any way to recover the data from my file level backup without the archive logs.

i personally think it is inconceivable that Oracle would design their database such that losing your archive logs would render a backup completely unrecoverable. i can think of a specific case where this is stupid and that is if your tape with the archive logs on it goes bad (is dropped, is lost, whatever).
Re: Assistance with recovering a database? [message #298637 is a reply to message #298616] Wed, 06 February 2008 22:48 Go to previous messageGo to next message
varu123
Messages: 754
Registered: October 2007
Senior Member
What error messages are you getting while opening the database?
Re: Assistance with recovering a database? [message #299659 is a reply to message #298616] Tue, 12 February 2008 21:36 Go to previous messageGo to next message
monto
Messages: 60
Registered: November 2007
Location: DALLAS
Member
One should never backup active redo log files or control files.

you sure about controlfile Shocked
Re: Assistance with recovering a database? [message #299660 is a reply to message #299659] Tue, 12 February 2008 21:40 Go to previous message
ebrian
Messages: 2794
Registered: April 2006
Senior Member
monto wrote on Tue, 12 February 2008 22:36
you sure about controlfile

I believe Ana meant simply using an O/S copy command for the control file while the database is running and not using the appropriate ALTER SYSTEM or RMAN commands to make a backup of the control file.
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