Re: Is this method of offline backup OK?

"Sean M" <smckeownNO_at_BACKSIESearthlink.net> wrote in message news:3C8F0E4E.77831FA5_at_BACKSIESearthlink.net...
> "Howard J. Rogers" wrote:
> >
> > "Sean McKeown" <smckeownNO_at_BACKSIESearthlink.net> wrote in message
> > news:3C8ECE31.95CA84FF_at_BACKSIESearthlink.net...
> >
> > > And a really bad idea to backup as a general practice. Oracle
> > > recommends against backing up your online redo logs.
> >
> > No it doesn't.
>
> Not to sound like a couple of 5-year-olds arguing here, but yes, Oracle
> most certainly does recommend against backing up online redo logs. See
> the Backup and Recovery Guide (in the 8i book it is on p. 3-10). It
> says:
>
> "Although it may seem that you should back up online redo logs along
> with the datafiles and control file, this technique is dangerous. You
> should not back up online redo logs for the following reasons:
>
> The best method for protecting the online logs against media
> failure is by multiplexing them, that is, having multiple log members
> per group, on different disks and disk controllers.
>
> If your database is in ARCHIVELOG mode, then ARCn is already
> archiving the redo logs.
>
> If your database is in NOARCHIVELOG mode, then the only type of
> backups that you should perform are closed, consistent, whole database
> backups. The files in this type of backup are all consistent and do not
> need recovery, so the online logs are not needed."
>
> If you have a more authoritative source for what Oracle recommends than
> the company's own documentation, I'd love to see it.
>

It's in the Oracle Backup and Recovery course material (which I teach regularly):

"Note: it is not necessary to include the online redo log files as part of a whole database backup, if the database has been shut diwn cleanly, by using a normal, transactional or immediate option. However, in cases where it is required to restore the entire database, the process is simplified." Chapter 4, page 5, under the heading "Closed Database Backups'.

>
> > It says absolutely never to back them up when taking *hot*
> > backups, but states that backing them up for a cold, whilst
> > technically not necessary, can make restoration easier.
>
> The above recommendation makes no distinction between hot and cold
> backups.
>
> > >See the Oracle
> > > Backup and Recovery Guide. Backing up online redos is dangerous
because
> > > you may 1) accidentally restore them after a crash, overwriting
> > > transactions in the existing online redos
> >
> > If you are performing COLD BACKUPS then you've lost those transactions
> > anyway, assuming that you are taking cold backups because you are not in
> > archivelog.
>
> What do you mean "lost those transactions anyway"? There is absolutely
> no loss of transactions in a cold backup - all redo information is
> written to the datafiles during a clean shutdown. The online redo logs
> after a clean shutdown contain no transactions needed for recovery - no
> transactions are "lost."
>

You've missed the point. The man is in NOARCHIVELOG mode. Therefore he loses those transactions anyway, since in that mode, recovery is to the time of the last backup, not the time of the failure.

> > The subject of this thread you may note is OFFLINE (ie, cold)
> > backups. And given the list of V$ views the original poster included as
> > part of his backup routine, I took it as obvious that the man is not in
> > archivelog mode.
>
> Please, explain why this is "obvious." I was most definitely assuming
> the user was in ARCHIVELOG mode.
>

Look at the list of v$ views the original poster was using before taking his backup. Do you see any mention of v$archive_log there? If you're going to take a backup, and you are running in archivelog mode, don't you think you should know what archives you should include in the backup?

HJR
> Regards,
> Sean
Received on Wed Mar 13 2002 - 13:23:41 CST