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Re: clustering and high availability?

From: Daniel Morgan <>
Date: Thu, 10 Jun 2004 17:39:58 -0700
Message-ID: <1086914413.599812@yasure>

Michael Austin wrote:

> Daniel Morgan wrote:

>> Mike wrote:
>>> We're starting a project at work moving VSAM to RDBMS. The choice
>>> is between DB2 and Oracle. It seems like the Oracle RAC is a better
>>> cluster choice with it's share everything rather than the DB2
>>> share nothing. Please post some opinions on this and/or other
>>> points of difference/intereste between the two DBMS.
>>> Mike
>> Before you make this decision you need to test your application
>> in a RAC environment and see how the memory interconnect works.
>> Assuming it is a well written scalable application consider the
>> following:
>> Shared Everything:
>> The more nodes I add the mean time between failures goes up
>> Shared Nothing:
>> The more nodes I add the mean time between failures goes down
>> Shared nothing makes the problem worse ... not better
>> Shared Everything:
>> Change the number of nodes and no change need be made to the
>> database.
>> Shared Nothing:
>> Change the number of nodes and bring the server down while you
>> re-federate the data.
>> DB2 is not in the ballpark unless running on OS/390 where it
>> is, in fact, shared everything. If shared nothing was better
>> you'd think IBM would have used it on OS/390 too: They didn't.
>> But who can afford to cluster mainframes?

> According to technical sales reps, RAC in a clustered environment only
> worked as intended - with 100% database availability across a cluster -
> on OpenVMS and Tru64 (5.1+)... say what you will about dinasaurs, but
> this is a technology that has been around for 20+ years now and no one
> has been able to duplicate it.
> It is still the only platform(s) that have true direct concurrent disk
> access 100% of the time(none of this NFS or active-passive crap). I
> have seen what happens to filesystems where more than one node tried to
> access a logical disk volume via a SAN or direct SCSI interconnect on
> those "other" operating systems and it ain't pretty...
> And if you want REAL clusterability you can still get Oracle Rdb
> (formerly DEC Rdb) for OpenVMS - why do you think one of the niche
> markets for this database and OS is stock market trading??? Because
> they don't want it to go down.
> Michal Austin.
> OpenVMS biggot :)
> but I can still unix and windows with the best of them...

Anytime you want to come to my lab I will be happy to give you four hours to try to bring down an 8 node cluster with RedHat Linux and a NetApp F810 Filerhead NFS mounted.

No one's done it yet.

Daniel Morgan
(replace 'x' with a 'u' to reply)
Received on Thu Jun 10 2004 - 19:39:58 CDT

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