Bob,
Yes... For Business Continuance (HP) or SRDF (EMC)
kinda solutions it is becoming an urban Legend. I will
give you an example...
1.2 TB usable disk spsce by HP's XP disk solution
costs us almost 800 K USD , that too after all kinds
of discounts.
Like John said, considering it saves a whole lot of
trouble and kinda fun to have around, it is
invaluable...provided you can persuade damagement to
part with that kinda money..;)
Cheers,
RS
- "Freeman, Robert " <Robert_Freeman_at_csx.com> wrote:
> John,
>
> Yes, and I could kick myself for not thinking of
> this, mirrors can be a most
> excellent alternative to backups both production and
> after a recovery. Of
> course, it can be an expensive alternative as it
> requires you to have
> 2x disk space... :-)
>
> But disk is cheap, right...?
>
> Or is that yet another Urban Legend???
>
> RF
>
> Robert G. Freeman - Oracle8i OCP
> Oracle DBA Technical Lead
> CSX Midtier Database Administration
>
> The Cigarette Smoking Man: Anyone who can appease a
> man's conscience can
> take his freedom away from him.
>
>
>
> -----Original Message-----
> Sent: Monday, March 18, 2002 1:18 PM
> To: Multiple recipients of list ORACLE-L
>
>
> Hi all,
>
> Notice the renamed heading - this thread has really
> taken off!
>
> Coming back to the issue: While I agree that you
> should not open the
> database until after you backup (hot or cold), I am
> still rooting for a hot
> backup. If you know the application well enough, you
> can perform 'selective
> hot backup' of a required set of tablespaces that
> you know will be changed,
> and continue hot backup of the others after the
> database is opened up. In a
> cold backup situation, the whole database is down
> for backup (including
> large TEMP tablespaces - 13Gb out of 130 Gb on one
> of my Production Apps
> databases!) for a longer duration than is necessary,
> which does not look too
> good on your availability reports. (And also
> remember to switch logfiles so
> that archivelogs are generated prior to release to
> users).
>
> Having said all that, a soft mirror that can be used
> exclusively for backup
> is invaluable. The whole database can be put in
> backup mode for a short
> time, the mirror 'broken' and the database backup
> ended. The mirror can then
> be used for backup to tape. In addition to this, you
> also have an online
> backup available (until the resilver starts) and you
> work off this disk
> backup for producting clones. Let me say that again
> - Invaluable!
>
> John Kanagaraj
> Oracle Applications DBA
> DBSoft Inc
> (W): 408-970-7002
>
> Grace - Getting something we don't deserve
> Mercy - NOT getting something we deserve
>
> Click on 'http://www.needhim.org' for Grace and
> Mercy that is freely
> available!
>
> ** The opinions and statements above are entirely my
> own and not those of my
> employer or clients **
>
>
> > 1. You do not open the database to users until
> AFTER you do a
> > backup (hot or
> > cold, dosen't mater) at point t2.
> >
> > 2. There is a method of recovering a database (8i
> +) after
> > RESETLOGS has
> > been
> > issued with archived redo logs. I discussed it in
> my DBA
>
> > > > * You *have* to take a COLD backup of the
> database after using
> > > resetlogs.
> > > > (Not required - a Hot backup and archive logs
> is
> > adequate. All hot
> > > backups /
> > > > archive logs prior to that are invalid,
> though...)
> > >
> > > Consider the following:
> > >
> > > Time:
> > >
> > > t0: database restored
> > > t1: database opened with RESETLOGS
> > > t2: hot backup started ( database in archive log
> mode )
> > > t3: users input very important transactions
> > > t4: database crashes, and must be restored
> > >
> > > How will you recover the transactions from time
> t3?
> >
> > As long as the online redologs are available, this
> should be
> > no problem. I
> > have successfully recovered databases where a log
> switch did
> > not occur and
> > recovery had to use an online redo log. (I am
> assuming that the lost
> > datafiles will be restored from this hot backup
> fresh off the tapes)
> >
> > On the other hand, if the online redolog is hosed
> you have lost the
> > transactions anyway, _regardless_ of the fact that
> a Cold
> > backup was taken.
> > Then you will have to go back to the _previous_
> incarnation
> > and redo the
> > restore and then perform a ccf/resetlogs (i.e.
> back to square
> > one). If you
> > have a Cold backup, you restore the cold backup
> and go on
> > with life. I.e. in
> > both cases (availability of cold or hot backup,
> lost online
> > redo log), you
> > have lost transactions...
> >
> > Additionally, with a Hot backup and depending on
> what was
> > lost, you can at
> > least perform tablespace/datafile recovery . With
> a cold
> > backup, you will
> > have to restore the whole database....
> >
> > The point I was trying to make was that a Cold
> backup after a
> > RESETLOGS does
> > not serve anything. Maybe there is still a gotcha
> I have not
> > been able to
> > figure out, so Backup/restore Gurus: take a bash
> at this
> > logic! I would love
> > to be corrected.
> >
> > (Btw, the previous recovery scenario was on 7.3.4
> - things could have
> > changed since, and I have not been able to test
> that out...)
> >
> >
> > John Kanagaraj
> > Oracle Applications DBA
> > DBSoft Inc
> > (W): 408-970-7002
> >
> > Grace - Getting something we don't deserve
> > Mercy - NOT getting something we deserve
> >
> > Click on 'http://www.needhim.org' for Grace and
> Mercy that is freely
> > available!
> >
> > ** The opinions and statements above are entirely
> my own and
> > not those of my
> > employer or clients **
> >
> >
> > --
> > Please see the official ORACLE-L FAQ:
> http://www.orafaq.com
> > --
> > Author: John Kanagaraj
>
=== message truncated ===
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Received on Mon Mar 18 2002 - 16:34:18 CST
