Linux mainframes beat PC servers on energy efficiency

Supermarket Tesco is considering...

Supermarket Tesco is considering deploying mainframes to reduce its carbon footprint. They may well be greener than data centres full of PC servers, but will IT directors start buying mainframes again to improve data centre energy efficiency?

IBM has worked hard over the past 12 months to sell the green potential of its mainframes. The argument is simple enough. Mainframes can do more work per kilowatt of electricity consumed compared to clusters of Unix and Windows servers in a data centre. While a single mainframe consumes more electricity than a single blade server, hundreds of blades are needed to achieve the equivalent computational throughput of a mainframe.

Research from analyst Robert Frances Group backs up IBM's claims. Its calculations for a large US retailer found that a monthly power bill of $30,165 for UNIX servers could be reduced to $905 for a z-series mainframe, representing over $350,000 in power costs annually.

Businesses assessing the mainframe need to buy IBM's z-series hardware equipped with a processor called IFL (Integrated facility for Linux), which runs Linux applications. The IFL processors are priced at $125,000 per unit, but Phil Payne, analyst at Isham Research, says users should be able to negotiate a price of about $30,000 each.

For existing z series users, this additional fee may be a worthwhile investment, allowing them to gain power efficiencies by moving Linux applications onto the IFL on the z-series mainframe.

While the numbers make sense on paper, few companies are following Tesco in looking at the viability of bringing back mainframe computing to reduce their carbon footprint.

Rakesh Kumar, vice-president at analyst Gartner, says, "I think it would be a brave user who would consider replacing Unix servers with mainframes running Linux." However, for businesses already running mainframes, Kumar recommends IT directors negotiate a good price for the IFL and software licence charges. If the price is right, he says, "It may well make sense to put the new applications on the mainframe, otherwise, stick to PC servers," he says.

IBM has seen growth in demand for mainframe applications. ""We are not seeing much interest in Europe, but we are getting new customers in China and India for the z-series." Douglas Nielson, a systems analyst at IBM, says Linux on the mainframe is quite mature. "Linux is a big driver for mainframe growth. 20% of new mainframe capacity is for Linux workloads." He says many businesses already have the IFL processor to allow them to run Linux.

So if businesses already run z-series hardware and have licensed the IFL Linux processors, they could look at moving some Linux applications onto the mainframe. Clearly, the mainframe is not going to suit everyone, and only certain applications can benefit from being run on Linux on a z-series. But, users could see significantly lower data centre power bills, where it is deployed.

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