Dan,
I think you're tapping right around the key issue here which
is what is the effect on the business of an application being down?
I've heard a lot of people calling for maximum availability
architectures where there is no single point of failure, but then we get
into the "what's this going to cost" part of the discussion & things
then get really messy. I've seen a VP complain that we were "halving"
the capacity of a disk array just so that we could have mirroring of the
drives. His contention was that we had not seen a drive failure in the
last 3 years, what made us think that one would happen in the next 3.
The problem isn't the technology, but the business implications thereof
that are not understood and consequently get into projects doomed to
failure in the first place. Now I've a current client with a WEB facing
application who has done the math and for them having a 4 hour down time
due to equipment failure is "acceptable". That being established a two
level standby configuration more than makes their expectations (one
standby local, the other remote). So, IMHO, maximum availability is
something that we have to define application by application with the
most critical application dictating the solution for the database
selected. Zero down time is like absolute zero or the speed of light
easy to define, impossible to attain.
______________________________________________________________
Dick Goulet / Capgemini
North America P&C / East Business Unit
Senior Oracle DBA / Hosting
Office: 508.573.1978 / Mobile: 508.742.5795 / www.capgemini.com
Fax: 508.229.2019 / Email: richard.goulet@xxxxxxxxxxxxx
45 Bartlett St. / Marlborough, MA 01752
Together: the Collaborative Business Experience
______________________________________________________________
________________________________
From: Dan Norris [mailto:dannorris@xxxxxxxxxxxxx]
Sent: Monday, January 21, 2008 12:53 PM
To: Goulet, Dick; mssql_2002@xxxxxxxxx; oracle-l@xxxxxxxxxxxxx
Subject: Re: RAC Vs Standby Database between Primary and Secondary Data
Centers
Dick,
Here's where I think we need to make clear what defines "high
availability" versus what becomes "disaster recovery". Many sites
want/need both. In my dictionary, I define high availability as a system
that can tolerate a failure of a single component without affecting the
application availability. There's also "fault tolerance", but that
starts to get into a whole other world, so let's put that out of scope
for now. Disaster recovery in my book is defined as a system that can
handle failure of a data center or geographic location without affecting
application availability. I acknowledge that many if not most disaster
recovery solutions do have some outage associated with their failover,
but that outage is generally shorter than the time required to
restore/recover the primary site at an alternate location.
Having said that, I don't disagree with your comments, but felt the need
to point out that high availability does not necessarily equal disaster
recovery. Also, I submit that RAC is not primarily designed as a
disaster recovery solution. As another poster mentioned, RAC does have
some support for "stretch clusters", but they are not widely used and
the MAA still recommends standby database in combination with RAC (at
least the last time I read it).
To the OP, I think the MAA has some good ideas if you're looking for
architecture decision points. It is online at
http://www.oracle.com/technology/deploy/availability/htdocs/maa.htm.
Dan
----- Original Message ----
From: "Goulet, Dick" <richard.goulet@xxxxxxxxxxxxx>
To: mssql_2002@xxxxxxxxx; oracle-l@xxxxxxxxxxxxx
Sent: Monday, January 21, 2008 9:24:26 AM
Subject: RE: RAC Vs Standby Database between Primary and Secondary Data
Centers
Bob,
RAC is not a High Availability solution in and of itself. A RAC
system must have all servers in the same physical location which leaves
you vunerable to earth quakes, fires, etc..... Standby database is
there to protect you against these types of disasters by placing an
identical copy of your database in a separate physical location that
presumably will not get hit by the "9/11 factor" at the same time. The
first thing you should do is determine what your trying to protect
against and then plan accordingly. RAC will protect you against a
single server failure in your local data center. Standby can protect
you against a single server failure as well, but adds protection for a
9/11 incident at the same time..
______________________________________________________________
Dick Goulet / Capgemini
North America P&C / East Business Unit
Senior Oracle DBA / Hosting
Office: 508.573.1978 / Mobile: 508.742.5795 / www.capgemini.com
Fax: 508.229.2019 / Email: richard.goulet@xxxxxxxxxxxxx
45 Bartlett St. / Marlborough, MA 01752
Together: the Collaborative Business Experience
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