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RE: RAC (Real Application Clusters)

From: Scott <oraracdba_at_yahoo.com>
Date: Fri, 27 Sep 2002 14:51:35 -0800
Message-ID: <F001.004DBCA5.20020927145135@fatcity.com> 





Greg, For the most part RAW is still a requirement for
RAC. There are more Cluster File system Options now
then there where 6 months ago.



Windows/2000 - Oracle now provides a CFS. I believe
you can download it from OTN. I don't have NT
installed so I can't comment on its reliability or
stability.



Linux - Sistina has a CFS at $1000/node, Polyserv has
a CFS and Oracle is currently developing a CFS for
Linux. Sistina is certified for Oracle9i R1 and R2. I
am not sure about Polyserv but I think it is
certified. I currently use raw devices on Linux but
should be installing Sistina sometime in October.



AIX - has a CFS and it is certified by Oracle. Not
sure if this for HACMP or RS6000/SP or both. 



HP - I don't think there is a CFS available for HP/UX
but their newly acquired Compaq TRU64 and OpenVMS has
a CFS. HP is eventually doing away with TRU64 so maybe
they will roll this technology into their HP/UX MC
cluster software.



Solaris 2.7 and lower you will have to use raw
devices.



Solaris 2.8 and greater you can use Veritas DBE/AC
3.5, This package includes the Veritas Cluster Volume
Manager, Cluster File System, Oracle Disk Manager
(ODM, Formerly known as Quick/IO qio), and thier
Cluster Server. This software currently supports
Oracle9i R1 and R2. This software configuration is
only supported on EMC 8XXX series towers(firmware
5567.35.20 or higher) and the Hitachi HDS 9910 and
9960 series( firmware 01-16-40-00/00 or higher). It
also recommended you use JNI controllers. Your disk
drives will also have to support SCSI-3 persistent
reservations and the PR flag has to be set on the
disks. The PR reservations are used for IO fencing in
the case of any split-brain conditions. I am currently
running RAC R1 and R2 using DBE/AC on SUN E6500's and
I have been very impressed with their product. I am
also running RAC on SUN e3500's using RAW and I have
found that the CFS has made my life much easier.



However if you choose to use shared Oracle homes you
can have problems with Oracle's IA. The IA doesn't
like to share logs and the other files the IA creates
and manages. You will have to create separate homes
for the agent or symbolically link these files to
local directories on these nodes. TRU64 has Context
Dependent Symbolic Link (CDSL) facility to separate
the $ORACLE_HOME/network directory from the shared
Oracle home installation. This is employed by using a
specific keyword in the filename (or a symbolic link)
that distinguishes the name of the current member node
of the cluster.



The other thing I want to comment on is the RAC is
implemented differently on different hardware. This is
not true. RAC is implemented the same on all hardware.
However there are some options that may implemented
based on a particular platform. RAC Guard is an option
that was specifically geared towards TRU64. In fact
Oracle thought it worked so good they licensed the
technology from COMPAQ TRU64 and implemented it in RAC
guard II so it is available on all platforms. It is
true that some platforms may implement clustering
better than other platforms, but this is at the
hardware level not necessarily at the Oracle level.



Don't forget SQLNET with TAF. Besides OCI you also
have to be able to use SQL*Net and thin drivers do not
use either.



Jesse, It's hard to say what questions to ask but if I
was just learning the product I would stick to a few
basic rules.



If it appears to work like magic ask how they got it
to work.


If it sounds to good to be true, ask to have them back
it up with facts.


Has anyone done this before?


Can they provide references?



The thing is don't be afraid to ask any question. It
is surprising how many people won't ask questions
because they think it is stupid but everyone else is
thinking the same thing. Also the answer may have
information for you to ask another question. 



The other thing is that if something is said that you
don't understand send it to this list. There is enough
talent on this list to know when the smoke is blowing
in California and it's not from the forest fires.



One last item. Don't look for RAC to fix your
application problems. If your application already has
problems RAC won't fix that problem and if your
application is not designed to scale then RAC will
provide high availability but not scalibility.



Scott








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Author: Scott
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Received on Fri Sep 27 2002 - 17:51:35 CDT












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