Once again, "Mainframe Linux vs. Unix"
By jsavit on Mar 01, 2007
First, Mr. Milberg says Today's new breed of smaller, cheaper mainframes, paired with the Linux operating system, look like an attractive alternative to Unix on RISC or SPARC servers. One wonders why he feels obligated to specify SPARC, when this applies equally to IBM's POWER - unless this is illustrating a pro-IBM slant (Mr. Milberg edits for IBM web periodicals and is an IBM partner), not to mention the obvious that "RISC or SPARC" is redundant, since SPARC is a RISC chip. Oh well, and we haven't even gotten past the first sentence.
He goes on to say This article compares the features and performance of Linux on the mainframe -- in this case, the IBM System z Server -- and compares it with Unix, in terms of its availability, features and performance. It does nothing of the sort; I wish it did. The article doesn't compare features or performance of mainframe Linux with anything other than by repeating stereotypes. One of the problems with mainframe Linux (and mainframe in general) is that IBM does not publish benchmarks describing its performance, even though they do that with all their other platforms. None of the public benchmarks that are familiar to the open systems world have yet been published. You can only speculate why! Open Systems require Open benchmarking.
Unfortunately, the article just rehashes stale stereotypes about mainframe performance. For example, it refers to "Maximum I/O bandwidth" without quantifying it. Many years ago mainframes certainly had superior I/O bandwidth compared to other platforms, but today's high end open servers use the same high end storage arrays from vendors like Hitachi, Sun, and EMC, and drive them flat out. Sun E15Ks were clocked at over 1 million disk I/Os per second, and over 18GB/second data transfer. I don't think mainframe Linux can get close to that, and possibly not z/OS either, but it could be proven if IBM were willing to run benchmarks in their labs and publish them. Those old assumptions are obsolete: it makes no sense to describe a high-end Sun server as "mid-range" in comparison to a mainframe when it has several times as many CPUs and several times as much RAM. Trying to be fair and not just a vendor zealot, I'm sure the same kind of comparison can be made using IBM's System p RISC machines. Mainframes are no longer the biggest iron in the data center, and the other benefits attributed to mainframes are now shared by other vertically scaled systems that apparently surpass mainframes in power at far less cost.
The article goes on to say Linux on the mainframe becomes a natural evolutionary step for their business' mission-critical applications. Virtually any application that runs Linux on Wintel computers will run on System z, with only a simple recompile. To the first part, one must ask "Why would that be a natural step?". The second part is simply false: while many open systems applications do in fact port easily to mainframe, it's far from "virtually any". Little things like big-endian vs. little-endian crop up, for example. And much of the software you expect simply won't be there, especially for vendor products - the ISV portfolio on mainframe Linux is a fraction of the size of what's available on Intel/AMD platform.
The article goes on to say if a company has a server farm of 200 distributed servers, it can be easily be consolidated into either one or two System boxes, hosting 60-70 Linux servers in a high-availability environment that can scale. Your definition of "easy: will vary, and this is only true if those systems are very under-loaded, as by and large those Linux servers are running on Intel or AMD chips that are faster than System z (rule of thumb: 4 Mhz of Intel == about 1 MIPS of mainframe - as far as such crude rules go). Just do the exact same thing on a 4- or 8-CPU AMD or Intel server using VMware or Xen, at a tiny fraction of the cost, plus the ability to do things like VMotion that don't exist on the mainframe. We at Sun will be glad to sell you a nice server that will do that very well, and so will our competitors at HP, Dell, and IBM too. That's a good thing: vendor competition leads to better price/performance and innovation. By contrast, there is only one vendor you can go to for a mainframe - leading to monopoly price economics.
What else: VM mode allows for thousands of Linux guests per IFL and will probably be the best fit for most installations. VM is definitely the right way to run mainframe Linux if you're going to do that, but scale back your expectations by a factor of 10 or 100. Thousands of penguins per IFL? Aint gonna happen. (If you're wondering what an IFL is: that's an IBM CPU neutered so it can't run z/OS.)
Discussing the UNIX-ish environment on z/OS: The Unix implementation is not native, runs in EBCDIC mode and is just not the most popular of systems in IBM land With that I cannot disagree. It's certified as UNIX, but is alien to the rest of the z/OS environment, and barely used.
Under "Support" the article says If you are already using Linux, why would you want to migrate to Unix? It is more expensive to staff Unix engineers and administrators than their Linux or mainframe counterparts. Uh, well, it could be due to the superior support and capabilities in the Unixes, not a (possibly imaginary) price difference for the admins. Oh, and mainframe Linux engineers/admins are mainframe guys (by definition), and have to have both mainframe and Linux skills. Treat those guys really well if you find them: there aren't that many, and you won't be successful without their skills.
Under "Flexibility" he says Linux, being open source, lends itself to faster innovation, as well as more timely releases of bug fixes. The open source community delivers faster because it does not have to go through the endless development cycles of commercial-based operating systems. Let's point out the obvious here: Solaris is open sourced, so maybe you can apply this problem to AIX. And what about those pesky design and QA cycles. Do you really want to get rid of them? The conclusion is also wrong: look at the innovations in Solaris 10, such as DTrace, ZFS, Solaris Containers, and Fault Management Architecture. There's plenty of innovation in Solaris that Linux people have expressed appreciation of, and sometimes envy.
Regarding "Open", the article says: Anyone that has worked on AIX, Solaris and HP-UX, will tell you that Unix is certainly not Unix. On the other hand, the Linux distributions may have some differences, but the underlying kernel is the same. I'll say it again: Solaris is Open Source. And, the second part is quite wrong. The kernel levels in different distros are different. More important, the administrative tools and conventions are extremely different on the different distros. Even the selection of packages is different. Just as a skilled individual can go between different Unixes, a skilled individual can go between different Linuxes - but it doesn't "just happen" as this article misleadingly states. (For the record: I've worked with Red Hat, SuSE, Debian, Gentoo, Slackware, and Ubuntu - believe me, it's not transparent.)
More misleading stuff about zLinux software being free. Does the article really mean to imply that one can modify source code to WebSphere or Oracle if it's running on Linux? This comes under a bullet section titled "Price", which unfortunately omits the main cost factors: the price of the expensive hardware, the price for the hypervisor, and the price of the service contracts for the "free" Linux. Prepare for sticker shock. Combined with misleading stuff about mainframe security, when that's a property of the operating system (z/OS or z/VM), not the chipset it runs on.
Near the end of the article, the author says Most of the cons of moving to Linux are eliminated by running Linux on System z. Really? How has that been shown? For example, you cannot say that Linux will not scale as much as Unix on System z. Sure I can. It would be interesting to compare this to IBM's AIX/ESA for mainframe if it were still alive, or to the OpenSolaris port if that completes. You cannot make the argument that there is lack of hardware integration and support, as IBM provides that on the mainframe, unlike running Linux on Wintel. For a price, of course. And it's not called "Wintel", when the OS isn't Windows.
To put this in perspective: let's go back to the smaller, cheaper mainframes mentioned in the beginning. That is $95,000 for a single CPU rated at 28 MIPS, no disk, no operating system. Outstanding by the standards of traditional mainframe pricing years ago, but for perspective: I can emulate 30 MIPS of mainframe on my laptop using a program like Hercules, for a cost of maybe $1K or $2K. Let me say that again: I can use emulation software to pretend to be a mainframe - outperforming that $95K IFL despite a 50x or 100x performance hit due to using software to pretend to be silicon - and still outperform that "cheap" mainframe while spending only 1/50th the price.
There may be articles showing that mainframe Linux is a good thing, but this is not one of them.
I'm convinced that at best there is only very marginal applicability for mainframe Linux, as almost anything you can do with it can be done at a fraction of the cost on other platforms. I say this despite my respect for individuals I know who are working on it, and my nostalgia and respect for the platform, especially VM. I suggest to anyone considering this platform: Don't believe me or anyone else. Demand price/performance guarantees, public benchmarks, and real suitability for the applications you intend it for, and disregard the hype.