Mainframe Linux: Pros and Cons

Why would one want to move Linux to the mainframe (such as IBM’s z10)? There are many reasons – and many reasons not to. Computerworld Australia had a good article describing (in part) some of the reasons the insurance company Allianz did just that. IBM has been pushing Linux on the z series for some time, and Red Hat and SUSE offer Linux variants for that purpose.

One common reason to move to a mainframe is that Linux servers have proliferated in the data center, taking up valuable space and becoming quite numerous. When all you need for a server is the hardware and a low-cost or no-cost Linux, then servers start popping up all over the place.

A single mainframe such as the z10 can handle thousands of servers (a test done in 2000 put 41,400 Linux servers on one IBM mainframe). The replaced servers can then be eliminated from the data center, freeing up valuable space and reducing the workload of current system administrators.

A common instance is where the company already has a mainframe in-house, running COBOL applications. Thus, the purchase cost of a mainframe (in the millions of dollars) has already been absorbed. Such a scenario also makes the case for a new mainframe much more appealing, as it puts the enhanced power to work immediately.

Replacing thousands of Intel-based Linux servers with a single mainframe will reduce cooling costs, power costs, physical space requirements, and hardware costs.

So why would anyone not want to use a mainframe?

If there is not already a mainframe in the data center, purchasing a mainframe just for the purpose of consolidation can be too much – mainframes typically cost in the millions of dollars, and require specially trained staff to maintain. Adding a mainframe to the data center would also require training current staff or adding new staff. A new mainframe also requires a new support contract. All of this adds up to not just millions of dollars of additional cost up front, but additional costs every year.

Another consideration is the number of Linux servers in the data center that would be moved. If there are dozens – or a hundred or two – it may not be entirely cost-effective to focus a lot of energy on moving these servers to the mainframe.

A supercomputer such as HP’s Superdome (with its attendant iCap and Integrity Virtual Machine capabilities) would probably be a better choice to consolidate dozens of Linux servers. The costs are lower, and the power requirements are lower – and you can purchase as much or as little as you need and grow with iCap. Most companies also already have UNIX staff on hand, and adapting to HP-UX is not generally a problem if needed.

Another benefit is that a server such as the Superdome offers virtualization of not just Linux systems, but Microsoft Windows and HP-UX as well – and soon, OpenVMS as well.

Using a large Intel-based server can virtualize a large number of servers with software from companies like VMWare and Sun.

These options won’t necessarily allow you to virtualize thousands of servers – but then, do you need to?