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Re: Multiplexing Datafiles?

From: Adrian Shepherd <theshepherds_at_hotmail.com>
Date: Tue, 15 Aug 2000 19:59:16 +1000
Message-ID: <Tx8m5.89106$N4.2157364@ozemail.com.au>

Obviously you are expressing an oppinion but in more informed scenario it is quite possible for a database with a couple of GB of datafiles or less to generate much more redo that the size of the databse, there is no correlation whatsoever between the amount of redo generated and the size of the datafiles. I have often pondrered the suitability of mirrored datafiles in many environments, your failure to grasp this theoretical fundamental approach instead of archiving leads your argument to be too focused. Accept that the original poster and myself and probably many other experienced and broad minded DBA's do see a requirement for this and would still like to see it happen.

We should at least have the option. And I beleive Oracle stands to gain in offering a more comprehensive set of options , it broadens their suitability to more customers.

Of course it doesn't help if the current negativity feeds back to Oracle, to re-iterate , you may not see a reason to, but others do. You have technical arguments against it in your real world experience, but that is far from all encompassing.

"Howard J. Rogers" <howardjr_at_www.com> wrote in message news:39990d4d_at_news.iprimus.com.au...
>
> "Adrian Shepherd" <theshepherds_at_ozemail.com.au> wrote in message
> news:jyRl5.88176$N4.2136496_at_ozemail.com.au...
> > What if I want to multiplex datafiles in my database but not run in
> > ARCHIVELOG mode for some reason, perhaps because the database would
 generate
> > too much archive or if the database is a warehouse that isn't suited for
> > ARCHIVELOG mode ?
> >
> > Multiplexing datafiles seem's a good enough request for me, and more to
 the
> > point , redo logs DO NOT supply all the protection you need, perhaps you
> > meant archived redo ?
> >
>
> You'll have to explain why providing all the redo since the time of the
 last
> backup doesn't provide you with all the protection you require. I made no
> distinction between on-line or archived redo in that statement, and
 rightly
> so. I also talked about 'mirroring your redo'. Loose terminology, I
> guess -but since Oracle 8, it's been possible not only to mirror your
> on-line logs, but also to 'mirror' your archives -log_archive_duplex_dest
> for example. Again, I make no distinction between online and archived
> logs -the fact is, protecting ALL your redo is all you need to ensure
 total
> data recovery.
>
> Since it remains a fact that providing all required redo since the time of
> the last backup guarantees that you will never lose a single committed
> transaction, I don't quite see what extra protection you'd need or want.
>
> Your proposed solution seems perverse. Instead of generating gigabytes of
> redo each day, you want to mirror tens or hundreds of gigabytes of
 datafile.
> I know which I would prefer to do if disk space was tight.
>
> Whatever. The fact remains, wishlists notwithstanding, there is no
 facility
> in Oracle to mirror datafiles within a single database (standby databases
> etc are a different sort of technology entirely, and are designed to solve
> different problems), and neither does there need to be.
>
> You are of course entirely free to put the database back into noarchivelog
> mode, and use external hardware mirroring to protect your datafiles.
>
> Regards
> HJR
>
>
>
>
> >
> > "Howard J. Rogers" <howardjr_at_www.com> wrote in message
> > news:3995df0c$1_at_news.iprimus.com.au...
> > >
> > > "Rob Jolliffe" <rjolliffe_at_my-deja.com> wrote in message
> > > news:8n4295$mqp$1_at_nnrp1.deja.com...
> > > > Hi,
> > > >
> > > > I'm just beginning to learn Oracle, and I was reviewing some Email
> > > > regarding Raid5 vs Raid0 performance. It seems Raid 0 is
 significantly
> > > > better for performance - but you lose the redundancy of Raid 5 (or
 even
> > > > Raid 1).
> > > >
> > > > I was trying to also determine if in a data tablespace it is
 possible
 to
> > > > multiplex (mirror) datafiles the same way you can with a Redo log
 group.
> > > > I was totally unable to determine if you are or are not.
> > > >
> > >
> > > Absolutely not. Never has been, and there never will be -because it
 is
> > > entirely pointless. The reason for duplexing your data files is,
> > > presumably, to avoid complete disaster in the event that one of them
 dies,
> > > gets deleted, corrupted etc. That is precisely what the Redo Logs are
 there
> > > for. Provided you've kept all your redo since the time of the last
 backup,
> > > you can reconstruct any given data file up to the precise time of
 failure.
> > >
> > > So if you're mirroring your Redo, you have provided all the protection
 your
> > > data files ever need.
> > >
> > > (Conceivably, you can use external, hardware mirroring of data files
 to
> > > enable recovery to take place *faster* -you just break the mirror and
 use
> > > the good copy. No need to wait for all that Redo to be re-played.
 But
> > > that's a mean-time-to-recovery issue. It's certainly not necessary).
> > >
> > > > Can anyone tell me? I know you can stripe tablespaces - but can you
> > > > mirror them? Perhaps this requires creating two tablespaces and
 somehow
> > > > matching them?
> > > >
> > >
> > > Forget it. There's no such concept in Oracle, because the Redo does
 all
 the
> > > protection work we need.
> > >
> > > Regards
> > > HJR
> > >
> > >
> > >
> > > > Thanks very much
> > > >
> > > > -Rob
> > > >
> > > >
> > > > =============
> > > > From the desk of Rob Jolliffe
> > > >
> > > >
> > > > Sent via Deja.com http://www.deja.com/
> > > > Before you buy.
> > >
> > >
> >
> >
>
>
Received on Tue Aug 15 2000 - 04:59:16 CDT

Original text of this message

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