RE: Active/Passive "high availability"
- From: "Allen, Brandon" <Brandon.Allen@xxxxxxxxxxx>
- To: <jkstill@xxxxxxxxx>, <oracle-l@xxxxxxxxxxxxx>
- Date: Fri, 13 Apr 2007 10:45:37 -0700
I've noticed there seems to be some disagreement about whether or not
RAC is really a "High Availability" solution. There is no doubt that
Oracle advertises it as such:
E.g. from
http://www.oracle.com/technology/products/database/clustering/pdf/ds_rac
.pdf:
"Oracle RAC provides very high availability for applications by removing
the single point
of failure with a single server. If a node in the cluster fails, the
Oracle Database
continues running on the remaining nodes. Individual nodes can be
shutdown for
maintenance while application users continue to work."
And here:
http://www.oracle.com/technology/products/database/clustering/pdf/twp_de
signing_%20ha_systems_with_rac[1].pdf
On page 13 there is a graphic of RAC with a mirrored disk subsystem, and
again the claim of "No Single Point of Failure"
So, it seems to come down to how you define a "single point". If you
look at the "database" as a single point, then yes there is a SPOF, but
if you look at it more granularly and consider that the database resides
on hardware with mirrored disks and multiple controllers, fibre
channels, fans, power supplies, etc. - then there isn't really a SPOF at
the database level either because it would really require multiple
failures to bring down the database.
A disaster such as flood, fire, earthquake, vandalism, etc. could easily
bring down the entire disk array at once, but that falls under the
category of Disaster Recovery, not HA and I think we all agree that RAC
is generally not a DR solution although I believe some are running RAC
with the nodes geographically dispersed in an attempt to incorporate DR
as well.
Regards,
Brandon
________________________________
From: oracle-l-bounce@xxxxxxxxxxxxx
[mailto:oracle-l-bounce@xxxxxxxxxxxxx] On Behalf Of Jared Still
A single RAC system with a single database (also a SPOF) is also not HA.
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