Re: Cold backup and Exp utility

Absolutely agree with Sybrand. Export is a useful adjunct to a physical backup strategy, but it's not a convincing replacement for it.

I wonder why he does nightly exports? I've recently come across a disturbing habit of DBAs to do totally unnecessary exports on the grounds that, in doing the export, Oracle is forced to read all the blocks of the database -and accordingly, it provides a check that no block corruptions have taken place (which, of course, a boring old physical backup using old o/s copy commands can't do for you).

If that's the only reason it's being done, then someone should have acquainted your DBA with the much more efficient DBVERIFY utility, which should, in my opinion, *always* be run after every operating system backup, against all the datafiles that have been copied. It checks every single block, and reports on any corruption found. Being applied to 'dead' datafiles, not online ones (though it can do that too), it's lightening fast, and doesn't impact on the performance of the live database.

Accordingly, I would drop back to (maybe) a weekly export, and schedule DBVERIFY every night instead.

Sybrand is perfectly correct that the main saving grace of an Export is that is gives you the flexibility you need to avoid having to do incomplete (or point-in-time) recoveries -which are a royal pain in the butt to perform, render the database unavailable for the duration, usually go wrong unless you have your wits about you, and result in data loss across the entire database. By restoring a table from an export, the database remains up, import is relatively simple to perform, and the data loss is confined to the single table involved.

Definitiely a 'both required' situation -but check the frequency of that export. Nightly sounds way over the top.

Regards
HJR "Sybrand Bakker" <postbus_at_sybrandb.demon.nl> wrote in message news:tbifolf5s9pg71_at_beta-news.demon.nl...
>
> "Jimmy Kan" <jimkan_at_earthlink.net> wrote in message
> news:Pt6u6.16574$Im6.1731302_at_newsread1.prod.itd.earthlink.net...
> > Hi,
> > A DBA setup a full Exp to run every night, once that is done the system
 will
> > shutdown the oracle and do a cold backup. Since we are doing a cold
 backup
> > every night, is it necessary to run the Exp utility? these two process
 takes
> > 9 hours all together.
> > Thanks
> >
> >
>
> They serve 2 completely different purposes.
> Exp is a *logical* backup.
> The cold backup is a physical one.
> The latter one is used for disaster recovery (hardware failure, power
 dips),
> the former one to prevent havoc when users accidentally drop a table, or
> delete some rows.
> If you have a disaster and you only have an export, you will deeply regret
> that, as you will be forced to recreate the database.
> If you deleted 32 rows from a 3 million row table and you don't have an
> export, you will deeply regret that too, as you will be forced to juggle
> with manual point in time recovery.
> In short: you need them *both* and you would better try to tune the export
> and maybe the cold backup.
>
> Hth,
>
> Sybrand Bakker, Oracle DBA
>
>
>
Received on Thu Mar 22 2001 - 03:52:24 CST