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The Practical Value Of Mainframe Linux
Sun Tzu writes: "Just in case you're wondering what else to do with the mainframe in your basement, here's some useful information to help you prepare a proposal to management." The article is clear and candid, noting things like, "In some discussions the issue of the S/390's 'five 9's' reliability is brought up. However, IBM's 99.999% uptime claim is for clusters of mainframes, not a single system." And no, running 40,000+ virtual Linux boxes is not that practical. Still and all, I wonder how much an S/390 will cost in 3 years ...
Part of the vaunted S390 uptime comes not only from the overt reliability of the the hardware but also from the reliability of MVS itself. You don't necessarily get the same reliability from replacing MVS with Linux. Moreover if you consider not only uptime but MTTR you will find that in the S390 arena those figures come at the expense of years and years of practiced discipline, at knowing just how to find and fix things quickly and exploiting a well understood break/fix methodology to remediate the problem. This is not necessarily the case with S390 Linux now and would require some years of experience to get there.
It seems that S390 Linux best serves service providers who can bill out chunks of a box to whomever wants a particular service hosted there. If this is the case I'm left wondering why it makes any difference what OS runs under the covers of a hosted service? There are two cases that we have to consider.
One - somehow the service provider can offer a cheaper service because there are zero or near zero OS licencing costs. If look at maintenance, labor, hardware leasing, etc. Is the OS licence a significant enough to lower the overall cost model of a hosted service. True MVS can be expensive but we've already assumed that the expense would be allocated to many customers.
Two - are there applications that are not supported on MVS or AIX but are supported on Linux in this space where a service provider would host a commercial service for a customer? Gee - I can't think of one in the realm of the SAP's, UDB's, Oracle's, Lawson's, Webserver's, etc... Or alternatively are there applications that can be procured from the vendor for significantly less if they are licenced for Linux and not anything else? Perhaps but not likely.
In the end I can't how this makes a great deal of business sense however interesting it is to do technically. Having said that there is one exception - the case of development + migration. I can a see a case being made for developing code in some other Linux platform or in an instance on an LPAR and then more or less easily being able to test and migrate it to production on a similar Linux platform in the LPARs. Today for example when we have to develop something in UDB/DB2 on say NT or Linux on a PC and then have to move that code upstream to an S390 there is a whole basket of problems that you can't avoid. It is possible that S390 Linux would reduce or even eliminate those assuming the DB or applications vendors themselves write more or less unified code for any Linux platform and the developer doesn't have to think about things like IO performance, locking, security and whatnot.
So, when I read about the S/390 version of Linux I started half serious (but half joking, too) to analyse replacing 24 low- to mid-range boxes with one S/390.
Aside from the cost of scrapping the 24 not-so-cheap machines and paying for a very expensive S/390, the maintenance costs are higher for a properly configured, working, redundant S/390 system. Much much higher. At least for now, it's just not a cost-effective proposition.
Some people, invcluding the author of this article have NO clue about true costs involved in a S/390 system. The system itself can cost as much as a mid to high end Sparc box. The processor is at least as powerful, but that's not why you'd want to use it as a web server. Mainframe has KICK BUTT I/O. Mainframe are MUCH more efficient at pumping I/O. You could use a mainframe to stream audio or video on your web site with copy, and a another copy could do the web serving. Also, the main cost of operating a mainframe is NOT just the hardware support, it's the software. We pay one vendor 20,000 a year just to get support and software updates! With Linux under VM, only thing you have to pay for is VM. You can load as many copies of Linux as u want on the mainframe. Also, you could probably use existing bus and tag and ESCON devices such as printers, tape silos and DASD as native devices under Linux. There are mainframe printers that can print 90 plus pages per minute! Granted, some of the mainframe reliability can be attested to software, but on our current system, we have 2 power feeds (you split those between two power substations), we have had RAID for YEARS longer then PC server's have had and we have been serving 2-3 million data requests a day and this was on a 10 year old mainframe, running DOS/VSE, a cousin of the first mainframe OS that MVS was to replace, but is still going strong. Our new one hasn't even scratched the surface of the power we have available. Oh and lest I forget, they can call themselves for service before they die. We have had disk packs go bad and we NEVER went down or knew we had a pack go out. Also, ESCON, a fiber based way to connect channel devices to the mainframe, can have a range of 4-5 MILES before needing a repeater (if one wants to lay that much fiber! Be cheaper to use the OSA ATM or Fast Ethernet adapter and do it with TCP/IP).Um, lessee, scheduled downtime is limited to changing time (we have to do it this way to preserve data integrity), some software updates do need a IPL too, OH and in my opinion, the MF can boot faster too! Gork
Gorkman
What that original article was really going gaga over was VM. I can understand that - VM is really sweet - but I doubt the configuration would be that useful.
However, I think Linux could be useful to mainframe sites like us. Here's why:
Very straightforward - except that the overhead of running OS/390 just to support Unix System Services is high.
Therefore I'd say that a probable - no, make that possible - future configuration for us is a partitioned S390 box with one slice running OS/390 and hosting the database and the other running Linux/390 and doing the web serving. Much lower overhead, I'd guess.
BUT there is no way places like ours will make a commitment to Linux/390 without substantial IBM support.