Mainframe Myths
Many techies are wary of mainframes because of the myths and mystique surrounding them. There are three main myths about mainframes:
1 They are hugely powerful.
2 They are very complicated.
3 They are ultra reliable.
None of these is actually true, let’s have a look at each of them and see what the facts are.
Firstly mainframes are not all that powerful; their clock rates are actually quite low because they have to propagate the clock over a long distance rather than just across a chip. They achieve much of their performance from smart pipeline and parallelism but like any parallel system this implies particular workloads. This workload type is the key to mainframe performance, given the right sort of load they do perform really well. This “typical” mainframe load is basically running OLTP type programs against simple hierarchical databases with text only output to a 80x36 text display. Mainframes have been set up to handle this load really efficiently which is where they get their reputation for performance. Give them a complex VB type application or even a complex database application and they struggle, in fact they can be a lot worse than a Windows Server.
Mainframes are very complicated from a hardware point of view but from a software perspective they are much the same as any other system. The operating system, languages etc are much the same as a Windows system. There are two main areas of difference however and these are in the connectivity and the middleware running on the mainframe. Whilst these are different they are not actually more complex, it’s just the terminology is different, in fact as pointed out at Life as a Reformed Mainframe Programmer in the .Net World MTS and CICS are very similar. I will write up a mainframe 101 to explain mainframe comms and middleware in MS speak to show this.
Mainframes are made up of lots of parts and connections and so are inherently much less reliable than a Windows server. Of course in real life the key thing needed to provide reliability is operations and maintenance not hardware or software and that’s what mainframe shops are great at. If you take a system (Windows or mainframe) and put it in a sealed environment with rigorous fault, error, upgrade and maintenance regimes and a static, well understood workload then you will get similar reliability. If you abuse the system in any way then the reliability will tumble. I have a really fun story about sex in a mainframe causing reliability problems that I have been told that I can’t publish so you will have to imaging the details!
Microsoft had a marketing campaign around reliability and five nines a few years ago which really annoyed me. It implied that if you used Windows then you would get five nines which is of course silly. Most downtime is caused by poor operational procedures rather than the software.
So whilst mainframes are different from Windows systems they have the same issues, limitations and requirements. We in the Windows world could learn a lot from the mainframes about operations, workload types and reliability which would address many of the issues that we have today on Windows servers. There is certainly no reason to either dismiss mainframes as legacy or be frightened of their supposed power and complexity because these are just myths.
Comments
- Anonymous
March 25, 2004
YES! Somebody else voices my opinions on mainframe reliability. The same can be said of any system that continuously performs a limited set of functionality (most unix servers, etc.) - Anonymous
April 05, 2004
The comment has been removed - Anonymous
April 05, 2004
The comment has been removed - Anonymous
April 05, 2004
Hello Michael,
I am suprised that, considering you experience, you make such statements without proper backing.
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"Give them a complex VB type application or even a complex database application and they struggle, in fact they can be a lot worse than a Windows Server."
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I do have to come across the first VB application on a Windows Server running the same magnitude of applications/data on a mainframe and serving the same amount of connections.
And truly what is "complex", handeling TB of data is no issue considering some of the systems I have managed as is running vast collections of conccurrent applications serving 100.000+ connections over dispersed locations in the world --- this is an actual situation within a large bank.
Let aside the security provided by RACF
My point, backup your statements before jumping to conclusions. Good luck with your Mainframe 101.
ps: I have knowledge and experience within the financial domain, covering most of the development and deployment lifecycle of applications on several platforms, ranging from Mainframe (IBM, HDS, etc), mid-range (AS/400, Unix, etc) and Windows Servers in various configurations (Wolfpacks). - Anonymous
April 05, 2004
The comment has been removed - Anonymous
April 05, 2004
Hi Michael,
"I'm suprised you put UNIX and AS/400 in with mainframes, hardly the same :)"
I had put them together as we have postioned them as midrange computers within our organisation (about 350 AS400, 400+ RS6000 and about 300 HP-UX), the mainframe environment consists of Tandem, IBM and HDS systems.
Do you have an idea when you will have finished your Mainframe 101.
I do think we are talking about the same; yes, indeed a mainframe will not suffice within a very rich GUI environment.
In my view mainframe will shift from the business layer to database back-end layer, most of the software we develop nowadays accesses the mainframe only for data operations. Much of the business logic is handled in the middleware and whereas presentation is concerned, it depends on the requirements of the end-user, thin client and/or web-based.
Greetings, - Anonymous
April 05, 2004
The comment has been removed - Anonymous
April 05, 2004
The comment has been removed - Anonymous
April 05, 2004
Totally agree about 1 provided CICS stays in there
With 2and 3 I am not sure. Mainframes are tuned for SNA and I spent years trying to get decent performance with TCPIP. I think there was a problem with the buffer sizes in VTAM but I could never get it to perform. Of course this was a long time ago and so maybe IBM have fixed the problem and got TCPIP to perform. If not then I dont see how you can get a web server to perform very well on a mainframe as a web server is very tightly coupled to TCPIP.
Love to try it and see, sort of thing I would go down to the labs and try when I was in IBM, alas Microsoft dont have a spare mainframe lying about, or at least wouldnt admit to it if they did! - Anonymous
April 05, 2004
I do see IBM gearing up to implement TCPIP on mainframes through the use of of OS/390 and Linux. IBM has made some major improvements in OS/390 concerning TCPIP performance, don't know though what is considered decent performance :)
check http://www.esj.com/columns/article.asp?EditorialsID=91
Greetings, going to bed, its late overhere :) - Anonymous
April 06, 2004
Thanks for the link. Totally totally agree in wrapping CICS as a web service, it is the way to go, I think you may have to have the web part of it hosted off the mainframe but it is the obvious way to go.
IBM has been saying for ever that they have fixed TCPIP performance, I am just dubious. I think there is something deep in the architecture of VTAM that causes problems. Anyway I think you are just better putting the Web server on windows, thats what it's good at.
The whole area of services and the mainframe is really interesting. I went and saw a customer who had made all their mainframe functionality into services and it worked really well.