Re: San-Based replication VS DataGuard replication

On Oct 6, 6:33 am, macdba321 <macdba..._at_gmail.com> wrote:
> On Oct 5, 7:04 pm, Palooka <nob..._at_nowhere.com> wrote:
>
>
>
>
>
> > Steve Howard wrote:
> > > On Oct 4, 5:27 pm, DA Morgan <damor..._at_psoug.org> wrote:
> > >> hpuxrac wrote:
> > >>> Sounds like you are just making up stuff.
> > >> Sounds like you weren't in San Francisco a week ago sitting in on the
> > >> excellent briefing Mark Townsend gave the Oracle Ace Directors. <g>
> > >> --
> > >> Daniel A. Morgan
> > >> Oracle Ace Director & Instructor
> > >> University of Washington
> > >> damor..._at_x.washington.edu (replace x with u to respond)
> > >> Puget Sound Oracle Users Groupwww.psoug.org
>
> > > I don't think this is an Oracle issue.  Oracle is just like an other
> > > app (I know it hurts to hear that) when it comes to stuff being
> > > physically written to physical disk.
>
> > > The disk subsystem controls what is physically written when and
> > > where.  Oracle merely twiddles its thumbs until it gets a return code
> > > from the storage subsystem.  The subsystem can do what it likes in the
> > > meantime.  If it hasn't made it to both subsystems, it will return an
> > > error condition to the application doing the write (Oracle in this
> > > case).
>
> > > I know for a fact that EMC SRDF does it this way, as we use it.
>
> > Well said.
>
> > Palooka
>
> Thanks to all for the valuable/insightful thoughts on my original
> post.
>
> It sounds like (in summary), that using DG will save network bandwidth
> as opposed to relying on SAN-based replication. However, CPU
> utilization on the secondary (disaster-recover) database will most
> likely be higher when using DG.

Well, don't forget there are also other options like logical standby. Oracle used to recommend the standby db be on identical hardware as primary, probably for this reason, as well as capacity on the standby has to be able handle when it is actually flipped over to.

>
> Also, there is a quote in "Oracle Data Guard in Oracle Database 10g -
> Disaster Recovery for the Enterprise" that reads:
>   "Data Guard allows the administrator to choose whether this redo
> data is sent synchronously or asynchronously to a standby site."
>
> Can anyone think of any instance when the disaster-recovery database
> would not be usable in the event of an emergency if you were relying
> on SAN-based replication??
>
> Thanks again.

I've seen the FAL process get confused due to unknown errors, probably network transmission errors. How the SAN would handle these sorts of situations is beyond me. Does it sit there and retransmit continuously? Would stopping your primary database because of a problem on the network or the standby be an emergency? I know my damagement thought that wasn't too cool...

jg

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