Re: Question about Archivemode

"Howard J. Rogers" <howardjr2000_at_yahoo.com.au> wrote in message news:ah4rcd$en2$1_at_lust.ihug.co.nz...
>
> "Howard J. Rogers" <howardjr2000_at_yahoo.com.au> wrote in message
> news:ah4r3k$ecu$1_at_lust.ihug.co.nz...
> >
> > "Ryan" <rgaffuri_at_cox.net> wrote in message
> > news:R4lZ8.92701$%%2.3951689_at_news2.east.cox.net...
> > > Ok this is a really basic Backup and Recovery question.
> > >
> > > If someone drops the system tablespace, ie, an intruder.
> > >
> > > Is it possible to perform a backup from the redo logs
> >
> > I'll stop you right there, and say that the question as posed doesn't
make
> > sense. You don't backup anything 'from' the redo logs. You use redo logs
> to
> > recover a copy (ie, a backup) of a datafile.
> >
> > >in you are not in
> > > archive mode or have any software like RMAN installed? Or do I have to
> > > recover from my last cold backup?
> > >
> >
> > The rules are exactly the same, whatever tablespace you are talking
about
> > (with the exception of temporary tablespaces). SYSTEM is no different
from
> > DATA or TOOLS in this respect. Either you can apply an uninterrupted
> stream
> > of redo from the time a backup of the datafile was taken to the time the
> > rest of the database is at, or you can't.
> >
> > If you're not in archivelog mode, then the chances of you being able to
> > supply such an uninterrupted redo stream is vanishingly small.
Therefore,
> > you won't be able to bring the backed-up datafile into synch. with the
> rest
> > of the database, and therefore the database can't be made to function
> > properly.
> >
> > How then do you get the database consistent and useable? By restoring
the
> > entire database from your last cold backup, as you say.
> >
> > There is one scenario where, despite not being in archivelog mode, you
> might
> > get away with a complete and perfect recovery: if the continuous stream
of
> > redo you require still happens to be sitting in the online logs. If you
> have
> > 5 online redo log groups, which switch every half hour, then you have
2.5
> > hours of redo available to you. So if you backed up last night, opened
the
> > database at 9.00am, and the intruder swiped the system tablespace at
> > 11.00am, you're doomed.
>
> BONG! I meant to say 12.00 noon.... you've 2.5 hours of redo available,
and
> he swipes it three hours after the database is opened... *then* you're
> doomed. 11.00am would be OK, because (despite my pathetic maths) that's
only
> 2 hours after being opened for business, so the required redo should still
> be available.
>
> Sorry. (Walks away muttering to himself.... "9+3=12, not 11", "9+3=12, not
> 11")
>
> Regards
> HJR
>
> >But if he swiped it at 9.45am, the redo required to
> > recover the backup of the system datafile is still available in the
online
> > logs, so you could just restore that one file and do a recovery on it.
> >
> > Clearly, there's no guarantees, though, that the required redo would be
> > available. Only archivelog mode can make that guarantee.
> >
> > Regards
> > HJR
> >
> >
> > > For those of you who saw an earlier post of mine... no this did not
> > happen.
> > > :)
> > >
> > >
> >
> >
>
>

thanks howard... my articulation is atrocious.. I meant use the redo logs to recovery. Sorry, but thanks for the explanation... didnt recall it in all that much detail.

Another question. We are using a tape backup. I do not know how these things work. If the database was to get destroyed for some reason, but the hard drive is good.. will I need to reformat the hard drive and reinstall all oracle products to get my backup with a tape or can I just grab the datafile, redo log files, control files... etc.. Received on Wed Jul 17 2002 - 18:25:27 CDT