Java on mainframes

Question

I work for a large corporation that runs a lot of x86 based servers on which we run JVMs.

We have experimented successfully with VMWare ESX to get better usage out of our data center. But these still consume a lot of power per processing unit.

I had a mad idea that we should resurrect mainframes, we could host either lots of JVMs or virtual machines.

Has anyone tried this? Are there any good cost-benefits?

Do you lose flexibility? E.g. we have mainframes in other parts of the company but they seem to have much more rigid usage of the machines.. lots of change control, long lead times etc

Gens

Answer 1

All this assumes you’re talking about Java on Z/OS and not running Linux VM’s on the mainframe to take advantage of the cost savings that come with fewer machines.

My thoughts on virtualization are at the end of this and it’s probably the route you want to look at but I’ll start out with Z/OS since it’s what mainframes are traditionally associated with and what I have familiarity with. I have some experience with mainframe Java.

The short answer is, it depends, but probably not. What exactly are your applications? The mainframe is a difficult environment compared to x86 servers. If you're running I/O-intensive workloads under something like Websphere, it might be worth it, assuming your mainframe is underutilized.

In my experience, Java is horribly slow on a mainframe but that’s because the system I used was set up for developer flexibility rather than performance. That just goes to prove performance tuning on the mainframe is usually much more complicated then on an average server since mainframes will be running many more workloads then a generic x86 server.

Remember that the mainframe is designed primarily for I/O throughput and can outperform any normal x86 server at that. It was not designed to do a lot of computationally intensive calculations so won’t outperform a small cluster of x86 servers if your doing a lot of math.

The change controls on mainframes are there for a good reason - if one x86 server has a problem, you reboot it. If a mainframe has a problem, every second that it’s down is costing the company money. You also have to take into account any native code your apps depend on or third party libraries that may use native code. All that code would have to be ported.

Configuration of a mainframe also takes a lot longer on average then on an x86 server. I would suggest that, if you want to seriously look into this, you make a better business case than power savings, such as tight integration with current business apps and start out small either with a proof of concept or a new application. One that is not business critical, that can be implemented to take advantage of the mainframes strengths.

IBM mainframes can also run Linux in either native mode or a virtualized environment similar to VMWare. Unless your company is the exception to the rule, your Linux instances would run as virtual machines. I haven’t had much experience with this but, if your app depends on no native code and runs under Linux, it would probably work on a mainframe running Linux. For more info about Linux on mainframes see this link.

Schizont

I wasn't sure whether the VM route (on a mainframe) or on the OS would be better. It sounds like the VM route would be better. Selling Thanks. – Gens

z/VM is the way to go. We have had a z800 running tens of thousands of RHEL (RedHat) LPARs side-by-side. @Jared, I cleaned up your one-paragraph answer to assist readability :-) One point - the Linux running under zLinux is either RHEL or SLES, so provided you can compile your app on the big iron, it will run there just fine, with all the features of the equivalent x86 versions. – Naevus

I'm just going back over the mainframe questions, doing a general cleanup, in case you're wondering why I'm looking at 6-month-old answers :-) – Naevus

@Schizont "the system I used was set up for developer flexibility rather than performance." What was your setup? IBM is incentivising Java on mainframe so there could be a very real business case unless the performance is really bad. Do you have any numbers? – Isaacs

@Isaacs I can't provide any useful numbers. Since I work for an ISV our system is set up for developer productivity not optimal resource usage and performance fluctuates a lot. I've sceen everything from CPU intensive programs running at 1/2 the speed they would on a 2.0 quad core desktop to 1/10 the speed. – Schizont

Answer 2

IBM makes a special Java co-processor that you should seriously consider. I would not run Java on the general engines as this may increase MPU charges for licensed software.

Deepdyed

Hmm. I forgot about the excessive software licensing costs. I guess even the potential hardware savings would be cancelled out by this. – Gens

It all depends on the size of the box you buy. – Ridley

Answer 3

We have extensive experience running Java under Windows, Linux and on IBM SystemI (or iSeries, or AS/400, depending on IBM's mood that year) minicomputers. It is my opinion that the mini-computer platform seems to deliver much less bang for your buck against modern multi-core x86 CPU's.

Note that Java benefits more readily from having multiple cores available than typical software today, because of it's inherently multithreaded nature - this would be even more true as you run multiple JVMs.

That said, you will typically be capable of getting many more CPU cores available with better bandwidth to access memory on a mini or mainframe, and better throughput on disk subsystems (overall) so these systems may very well scale much better as you toss more JVMs on them.

Wholesale

Answer 4

IBM allows this. Some of their mainframes can hold Java accelerator processors that run the bytecode natively for more performance. They also have DB2 accelerators, and possibly some for XML operations.

I've never gotten to play with any of them, but I'd sure love to.

Vagrom

I think that there is a certain class of application that this would work well for. I mentioned it to colleagues and they looked at me as if I were mad. But I reckon its worth a serious look. – Gens

If you're running a giant transactional system (i.e. a stock exchange or some such) I'm sure it'd be great. If you're just running a ton of web applications I'm not sure it would turn out to be worth it (except for ego!) – Vagrom

The Java and DB2 processors don't actually offer any better performance. The microcode has just been changed to limit what can be done with those processors, and IBM charges significantly less than for a general purpose processor. – Adagietto

zIIPs and zAAPs (DB2 and Java) CPUs also don't count towards your machines MIPS rating. This makes all software they's charged on MIPS cheaper. – Naevus

Answer 5

Though I've been in the Industry since 1975, I'm no longer sure what a "mainframe" is. My current development machine has four 3GHZ processors in it, 8GB of RAM, and 750GB of disk space (RAID 1, so it's really double that), and two 19-inch flatscreen monitors.

That's because I'm there on a contract. The employees all have much more powerful boxes than mine.

I understand that the server machines, especially the database servers, are much faster.

Mainframe?

Glottochronology

Having being in the industry since 1984 (and having used mainframes at university) i think this is a good point. By a mainframe I mean something that can cope with large bursts of I/O, manage and schedule lots of jobs etc. VMWare is good but the hardware isn't quite there yet. – Gens

A mainframe is a machine that can run 10000 Linux VMs at the same time. A desktop computer cannot do that. – Unroot

@Tom: what size VM? What's the level of activity? 5% simultaneously active? Would h10010.www1.hp.com/wwpc/us/en/sm/WF25a/… be a mainframe? Eight of them? Can I use more than one rack? – Glottochronology

I wouldn't say so. Take a look at IBM's zSeries: www-03.ibm.com/systems/z/hardware Up to 3TB of memory, 96 quad-core 5.2GHz processors. Of course the pricing is also "enterprisey": whirlycott.com/phil/2005/09/27/ibm-mainframe-pricing-models – Unroot

@Tom: so the z10 is not a mainframe because it can only handle 1.5TB of RAM? BTW, the HP link I posted earlier was just from a quick search. I think h20341.www2.hp.com/integrity/us/en/high-end/… is more what you would call a mainframe. BTW, I guess the definition must change with time, such that the "mainframes" in use ten years ago no longer qualify as mainframes. – Glottochronology

Answer 6

Depending on you workload this is worth looking at!

There are a bewildering number of options available to you just using the IBM hardware:

1. Its definately worth considering the add on java processors. (these are actually not that different form the standard cpus its just they are restricted to java jvm workloads -- and -- most importantly are excluded from cpu based software license pricing).

2. You can run multple Linux VMs each ruuning thier own Java app.

3. You can run multiple native VMs running thier minimalist operating system used to be called DOS but they change the name every couple of years. The software licenses are cheaper than the main OS, but it has very limited functionality which turns out to be an advantage if you are running self contained applications.

4. You can run in the monster z/OS environment either:-

a. Within USS (Unix System Services) which is pretty much a full UNIX OS running inside the parent z/OS.

b. Run your java app in its own started task (== unix daemon).

c. Run your app inside CICS. (Probably not as you need to use CICS/Java API where you would normally use Servlet/J2EE APIs so you app would require a rewrite.)

Probate

I no less about UNISYS - but they offer schitzophrenic machines which run Windows Server and there legacy OSes in the same box I understand they offer pretty good JVM support inside the legacy OSes. – Probate