Re: Minimizing backup induced downtime

On Jul 12, 5:23 pm, Alexander Skwar <use..._at_alexander.skwar.name> wrote:
> · rogergor..._at_gmail.com <rogergor..._at_gmail.com>:
>
> > Alex:
> >>Suppose you're doing a RMAN backup at 22:30. At 22:45 it's
> >>done, ie. also writing to tape is finished at that time.
> >>At 23:00, the server dies and the tapes are still intact.
> >>With that magical RMAN thing, how will you be able to recover
> >>anything that's changed in the database after 22:46? My, maybe
> >>ncomplete, understanding of how RMAN works, is, that it can
> >>take a backup of an Oracle database without the need for having
> >>it shutdown (thus a hot backup). But how will RMAN allow me
> >>to recover something, which hasn't been backed up?
>
> > I've done just such a test and it works magically. I'm beginning to
> > think that you either aren't running in archive log mode, or you don't
> > know what that is.
>
> I am running the databases in archive log mode and I know what it is.
> But the problem is, that the logs aren't backed up. They are, at best,
> backed up until 22:45. Then the backup is finished. Everything that's
> stored on the disks/in the database between 22:46 and 22:59 has not
> been backed up yet.
>
> It's possible that I don't understand something here. But how
> can you recover the database, so that it is in the state it was at
> 22:55? Remember, the archive log files are lost. I'm really
> interested - how can that be done? I mean, on tape (or on some
> other secure location/medium) there's the database the way it
> was up until 22:45, at best. Isn't it? From where does RMAN/Oracle
> pull the data about what has been done between 22:46 and 22:59,
> if archive logs aren't available?
>
> > Sooner or later your luck will run out.
>
> Hm. Not impossible. ACK.
>
> > What if the server dies
> > during your ZFS snapshot or your export? Then you have to go back
> > even farther?
>
> But isn't it the same with RMAN or "old school hotbackups running in,
> archive redo log mode"? Suppose you're doing a copy to a secure
> medium (tape/off site disk/whatever) only every 24hrs - how would
> RMAN/archive redo log be an improvement in this case?
>
> > I posted some helpful info in the other thread on places to look for
> > help with RMAN (sample RMAN scripts in $ORACLE_HOME/rdbms/demo) but
> > you clearly did not see that.
>
> Nope. I have seen that and sent you an email reg. this about 2hrs ago.
> I did not yet read the ressources you pointed me to. I'll do that
> tomorrow morning.
>
> > turn 40." It's not the age, it's the unwillingness to learn and apply
> > the better technology where it's appropriate that wrecks careers.
>
> Exactly. Where it's appropriate. As it is, I need to backup Oracle
> and some other directory. Those two need to be in sync. And here
> comes another reason against RMAN or even archived redo logs: As
> I wrote, the two directories need to be in sync. I take a backup
> of the directory and also Oracle every 24 hours. Suppose
> that the storage on tape is good (which is an entire different
> question...). What good would it do me in real life, if I could
> restore/recover the Oracle database to a PIT (point-in-time) it
> was 18 hours ago, when I cannot do the same to the directory?
> Yes, I know that there are setups, which would allow me to do
> even more snapshots, like NetApp filers. But we don't have that.
>
> It's all nice, that I can do a PIT of Oracle - but really, what
> do I do with that? Not in general or in a Oracle only world, but
> in the scenario I described.
>
> Alexander Skwar
> --
> It was a JOKE!! Get it?? I was receiving messages from DAVID LETTERMAN!!
> YOW!!
Alex:
>It's possible that I don't understand something here. But how
>can you recover the database, so that it is in the state it was at
>22:55? Remember, the archive log files are lost. I'm really
>interested - how can that be done? I mean, on tape (or on some
>other secure location/medium) there's the database the way it
>was up until 22:45, at best. Isn't it? From where does RMAN/Oracle
>pull the data about what has been done between 22:46 and 22:59,
>if archive logs aren't available?

Have you ever had to do media recovery on a restored datafile?

Roger Received on Thu Jul 12 2007 - 16:28:18 CDT