Re: Minimizing backup induced downtime

On Jul 12, 5:23 pm, Alexander Skwar <use...@xxxxxxxxxxxxxxxxxxxx>
wrote:
· rogergor...@xxxxxxxxx <rogergor...@xxxxxxxxx>:

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



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