Re: Multiplexing Datafiles?

Hi,

As the other poster implied, I'm not interested in mirroring data files for the purposes of backup - but rather for failover recovery. If a disk drive goes down which contains a data-file - and that drive is not mirrored in some way - the instance will go down (of course there are some circumstances where the instance will continue to run and you can rebuild that datafile "hot" - but not with the database schema I support - and unfortunately it's a canned product so that can't be modified).

Even if the circumstances are optimal (ie; You're there and you have a hot spare drive) - it might take some time to restore a large datafile and tablespace.

If it was possible to mirror data files (as some other DBMS are able to do) then the instance would remain online for the users.

I do ofcourse understand what and why redo logs are kept - I was just wondering about the possible existance of data file "Groups".

-Rob

In article <3995df0c$1_at_news.iprimus.com.au>,   "Howard J. Rogers" <howardjr_at_www.com> wrote:
>
> "Rob Jolliffe" <rjolliffe_at_my-deja.com> wrote in message
> news:8n4295$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.
>
>

--
=============
From the desk of Rob Jolliffe


Sent via Deja.com http://www.deja.com/
Before you buy.