The tao of managing virtualised servers

You can save time and money with virtual servers - it just takes some thought.

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Some customers are taking other tacks. At Radiator Express Warehouse, Carvalho employs what he calls a three-tier solution. He uses the tools that are already part of VMware's ESX, which he calls "awesome," but he backs them up with Dell Remote Access Controller, which monitors all the equipment in his physical servers, and WhatsUp Professional from IPswitch for managing his network.

What to virtualise

Holmes noted there are some myths about what you can and can't virtualise successfully. "Originally, when VMware was the first virtualisation product to really penetrate the enterprise market, you had people saying, 'Don't virtualise this or that,' " says Holmes. "That has somewhat changed." As users have become more comfortable with virtualisation, it's become clear that a lot more can be virtualised than some people originally thought.

For example, a lot of enterprises were reluctant to virtualise DBMS applications because they need so much memory, processing power and memory bandwidth.

But these days, advances in server technology, such as multi-core servers that can take a lot more RAM, have made database virtualisation more practical.

Ruven Cohen, CTO and co-founder of Enomaly, says that better hardware has a lot to do with the acceptance of virtualised databases. "On the early servers, when virtualisation was relatively young, your big stumbling block was what you could put through the server," he says. "With the latest chip sets from Intel and AMD, that is no longer an issue."

That said, in nearly every datacentre, there are some applications it isn't a good idea to virtualise.

For example, Carvalho runs his production database on Dell eight-way 6850 servers. "I would never virtualise those, because I would lose too much performance," he says.

Similarly, Jamey Vester, a production control specialist for Subaru of Indiana Automotive, says his company doesn't intend to virtualise its SQL Server cluster. Also, he says, "some of the specialised production and automation applications are very sensitive to the physical hardware."

The critical point is not that these applications are databases, but that they are large, resource-intensive applications. For example, AET's Stucker doesn't virtualise his company's enterprise database, which is an ERP and data warehouse system running on Informix on HP-UX and which Stucker calls "huge." "But we have all kinds of ancillary databases we have virtualised," he adds. "We have a number of SQL Server databases that are virtualised."

Generally, applications that heavily load their servers in terms of bandwidth or capacity are not good candidates for virtualisation - unless you get more powerful hardware.

Establishing and maintaining virtual machines absorbs resources (although how much depends on what kind of virtualisation scheme you use). Those resources come out of the same resource pool that supports the virtualised application. If an application is using 80 percent of a physical server's resources, it's not a good candidate for virtualisation unless you put it on a much more powerful server.

The licensing problem is stickier. Some vendors don't license their products to run on virtual machines. Sometimes this is done for business reasons, to keep control of the number of copies running in the enterprise. Sometimes, although more rarely, it is done because there are hard limits in the software that inhibit performance on a virtualised server.

In some cases, the vendor simply doesn't know how the product will perform in a virtualised environment and is trying to avoid possible performance problems.

Generally, software vendors are becoming more virtualisation-friendly, but you need to check the license before trying to virtualise an application.

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