Re: clustering and high availability?

From: Michael Austin <maustin_at_firstdbasource.com>
Date: Wed, 09 Jun 2004 21:26:48 GMT
Message-ID: <sgLxc.5205$c67.4657@newssvr23.news.prodigy.com>

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... Received on Wed Jun 09 2004 - 16:26:48 CDT