Re: backup versus export of db

Barry Roomberg wrote:
>
> metco_at_earth.execpc.com (Milwaukee Tool) wrote:
>
> >I've been told by a Value-Added-Resaler of Oracle that if i want to backup
> >an oracle 7 db, i should first do a full export, and then backup up the
> >exported file.
> >They said that a simple backup of the files used by oracle isn't good enough.
> >The reason given went something like this,
 

> > "while oracle is running, it leaves certain files open. Consequently,
> > if you do a simple backup of the filesystem on which oracle resides,
> > even if no db transactions are pending, you aren't guaranteed to
> > capture the complete, latest state of the data."
 

> >Can you shed any light on this statement? If basically true, what is really
> >meant by "leaving files open"? My interest in knowing goes beyond the
> >question of how to backup the db - I am also trying to decide if i there's
> >enough benefit to warrant mirroring the disk partition(s) that hold the db.
 

> >Thanks much for any help you lend.
 

> >Jon Detert, metco_at_execpc.com, 414.783.8527
>
> I can't BELIEVE the responses you have been getting on this one.
>
> One of the MAJOR benefits of Oracle is flexible on-line backups.
> This means you can backup the database while it is up and running,
> while people are applying transactions, while queries are running,
> etc.
>
> It can be a little bit pain in the but to set it up, but it is WELL
> worth it. I've been doing hot backups and restores with Oracle for
> SCO Unix for the last 4 years, and have done many restores for
> emergencies and testing, and have rarely had ANY problems.
>
> And the problems that I did have were never silent, ie: inconsistent
> transactions.
>
> I suggest to any of the people that told you that you can't do on-line
> backups go back to lurking, as opposed to spreading mis-information!
>
> Also, since you are using a VAR who has NO idea what Oracle can do, do
> you really want to trust him to help you (and take your money in the
> process)?

DITTTO. Oracle HOT backups have probably got to be one of the most misunderstood pieces of functionality I have ever encounterd. There are even vendors or integrators out there that say you can not back up Oracle datafiles using /bin/cp or /bin/dd. Where do they get this mis-information. I can tell you, they don't read the manuals.

Just be sure that when you are donig hot backups, the tablespaces/datafiles are in BACKUP mode before you copy the physical datafiles. Or, you will get error messages when you try to use them for restore. If you are doing full exports while the system is on-line, consider using the CONSISTENT option to maintain table integrity in your export file. If you are doing HOT backups, be sure to keep copies of your archived redo logs, at least back to your last cold backup. Or, you will be sorry when you find Oracle wanting to apply an archive log you no longer have on the filesystem or tape.

Test your backup procedures. Don't assume everything is working and find out during your restore that something is missing.

---
Neil Greene
Senior Oracle DBA / Unix System Administrator
SHL Systemhouse, Inc.  	LA Outsourcing Center 	
<HREF=mailto:ngreene_at_shl.com>