opinion: z/OS vs UNIX: Which Comes Out the Winner?

In a straight fight, which platform is better? Is it z/OS running on IBM's flagship Series z platform, or the ever popular UNIX operating system in all its flavours? We take a fresh look at the contenders.

If you want some good entertainment, get a few z/OS and UNIX® experts into a room and ask them which is better. I guarantee within seconds you'll have two warring factions passionately defending their platform to the death. It's great viewing - just don't give them weapons. An impartial opinion would be easier to find from fans at your local football game.

z/OS running on IBM's System z platform has been quietly running critical systems for decades, providing excellent performance, reliability and security. However many organisations are being wooed by UNIX, with its promise of lower costs, ease of use, and wider acceptance. So how do these two platforms really compare?

I'm throwing my hat into the ring. I'm going to take a broad look at the two platforms and the arguments for each. To do this, I'm going to leave out the technical arguments - no discussions over which is faster, or how they compare in various benchmark tests. Instead, I'm going to look at the basic arguments for each from the point of view of the user.

But before I start, let's clarify what we're talking about. When I refer to UNIX, I'm referring to UNIX operating systems used on larger servers (Linux, Solaris, HP-UX, AIX etc). However I'm not talking about z/OS UNIX Systems Services (USS).

So now that's done, take your seats. The show is about to start...

In the Blue Corner: The argument for z/OS.

Round 1: z/OS is more reliable.

For many years Mainframes have set the standard for reliability. IBM proudly states that Mainframes can achieve “five nines” (99.999%) availability, or around 5 minutes unscheduled and scheduled downtime per year.

However the reliability of UNIX is improving. A Yankee Group survey in 2008 found an average UNIX downtime of around one hour per year.

Of course a system's reliability is only as strong as its weakest link, which is rarely the processor hardware or operating system. So let's consider things like applications, systems software, and technical staff procedures. In these categories, Mainframes start to edge ahead. I've found Mainframe software in general to be more reliable than it's UNIX counterparts. Add to this the fact that Mainframe managers usually have stronger operational standards, and change management procedures.

I'll give this round to z/OS.

Round 2: z/OS is more secure.

Few people would dispute that z/OS is the most secure platform on the planet. It is the only platform that has obtained the Evaluation Assurance Level (EAL) 5 security rating. What's more, there has never been a reported incident of a mainframe being hacked or infected by a virus. Ever.

Another round to z/OS.

Round 3: z/OS is better at Large Workloads

Mainframes have traditionally been the enterprise workhorse, processing large numbers of transactions that in the past would leave UNIX systems gasping. For example, IBM has recently tested a single IMS subsystem processing 22,000 transactions per second.

UNIX servers certainly can't match this – yet. However this doesn't mean that UNIX applications can't process large numbers of transactions. In 2007 HP reported processing over 1,600 transactions per second using Oracle database. This capability can be further increased using clustering technologies.

z/OS gets extra points for being more scalable. Want to double your transaction throughput? Ask your IBM engineer to switch on more processors and you're away. Nothing else to do. A similar exercise with a UNIX environment will usually involve adding a few more UNIX servers to your cluster.

z/OS gets this round on points.

In the Red Corner: The argument for UNIX.

Round 4: UNIX is Cheaper

At first look this would seem to be a no-brainer. Mainframe hardware and software has always been far more expensive. However for large workloads, some analysts are challenging this assumption.

In 2006 Illuminata had IBM rubbing their hands in glee when they said that the Total Cost of Ownership (TCO) for System z mainframes was actually less than for equivalent UNIX servers. There was a catch: this was only for sites with 20-50 different applications. Illuminata argued that running multiple applications on one server saves on energy, software, network and people costs.

Distributed vendors disagree. HP has its own site that claims to calculate how much cheaper HP servers are to IBM Mainframes. With all these competing statistics flying around, it's easy for Mark Twain's statement about “lies, damn lies and statistics” to start floating around your head.

But whatever the statistics, it all has to come down to the individual site. For example, the software licensing bill for a z/OS system running 10,000 CICS/VSAM transactions a minute will be a fraction of an equivalent system running a mix of IMS/DB2 and CICS/Adabas. This is simply because the second system uses more software. Mind you, the possibility of z/OS being cheaper than UNIX is an interesting point if you're a large Mainframe site thinking about downsizing to save money.

These TCO figures usually concentrate on the cost to run a computer system, and leave out costs of software development, modification and maintenance. Many would agree that developing and maintaining a legacy Mainframe application takes more time and resources. This is because Mainframe applications:

• Have been around for longer, so are more complex.
• Use platforms such as IMS and CICS which are harder than equivalent UNIX platforms.
• Are written in legacy languages like COBOL, PL/1 and Assembler, which are more difficult.
• Are often critical to a business, so there's less tolerance for any failure. This means that any change must be carefully written, exhaustively tested, and double checked.

So after all of this, it seems reasonable to say that UNIX is far cheaper for small to medium sized application environments, and may also be for the top end.

UNIX pips z/OS in this round.

Round 5: UNIX is Easier

Few people would argue that UNIX is harder to administer and use. Computing graduates all come with a couple of years UNIX experience, and can quickly become productive. UNIX comes in many easy-to-install packages, so even small businesses with little UNIX technical knowledge can setup and maintain their own UNIX server.

Mainframe systems are hard. They are completely different to UNIX, and few computing graduates have ever seen a Mainframe. Every Mainframe technical person usually needs more education than their UNIX counterparts. And this education can be expensive and hard to find. IBM has made moves to fix these problems over the past few years, by:

• Porting languages such as C and Java to z/OS. Other languages such as PHP are on the way.
• Introducing tools to make z/OS administration easier – such as the CICS TS 4.1 Explorer, and z/OS Health Checkers.
• Introducing the zNextGen program to increase the number of graduates with Mainframe technical skills.

But despite all this, UNIX clearly wins this round.

Round 6: It's Easier to Find UNIX People

I don't think anyone would argue that its easier to find Mainframe technical staff.

A clear round for UNIX.

Round 7: UNIX has better connectivity and compatibility.

UNIX is an open platform, and talks well with the vast majority of other platforms that tend to follow the same rules (like Windows). However connecting to legacy applications on the Mainframe has in the past proven to be expensive and difficult, if not impossible.

Recent (and not so recent) Mainframe enhancements have made some progress here:

• Legacy applications can be accessed using Websphere MQ and SOAP.
• CICS transactions can be accessed using the CICS Transaction Gateway.
• IMS transactions can be accessed using IMS Connect.
• Mainframe files can be accessed remotely using FTP, NFS, and other standard UNIX file sharing features.
• Mainframe files can be accessed using software such as Samba.

However despite these advances, opening up your existing Mainframe applications to the world can still be a large task.

UNIX gets an additional advantage as its applications are easier to port to different environments – including z/OS itself (using UNIX Systems Services). Legacy Mainframe applications on the other hand aren't going anywhere.

Another clear round to UNIX.

Round 8: There's More Off-the-Shelf Software for UNIX

Most Mainframe applications are written in-house, sometimes using features of other application systems such as SAP, Hogan and Siebel. However end-user applications are everywhere for UNIX platforms, including a lot of freeware.

UNIX easily grabs this round.

The Final Decision

So after the final round, who wins? Well, that has to depend on who you are and what you need.

• If you need a smaller server platform with a ready-made software package, you'd be silly to go past UNIX.
• If you're writing a brand new application from scratch, it's hard not to be lured to UNIX. However if this application will be working with existing Mainframe applications or will process very large numbers of critical transactions, then the z/OS advantages become very appealing.
• If you have existing critical Mainframe applications, there are lots of reasons to keep them going. As far as security, reliability and the ability to handle lots of transactions, nothing beats z/OS.
• If you have a smaller, less critical Mainframe application, it may be a candidate for a move to UNIX.

UNIX is a trademark of the Open Group. Linux is a trademark of Linus Torvalds. z/OS, Websphere and AIX are trademarks of IBM. Other company, product, and service names may be trademarks or service marks of others.

David Stephens

LongEx Quarterly is a quarterly eZine produced by Longpela Expertise. It provides Mainframe articles for management and technical experts. It is published every November, February, May and August.

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