How many virtual machines is your server suitable for configuration?

Choosing just enough virtual machines, not too many, has been a dilemma for a given server. From the very beginning, it seemed easy to support these applications on a single physical server running a single virtual machine and running only one operating system.

Burton Group analyst Chris Wolf said, however, to ensure that the hardware can support the additional workload is the need for real skills, because the type of software running in the virtual machine environment is almost unlimited, each application for the host operating system And the hardware requirements are a bit different.

Ian Scanlon, IS Operations Manager at London-based Computacenter, a data center and IT services company with operations in most of Europe, said that integrating physical servers into virtual machines will of course save you money, but you can not do without compromising on application performance and no anger End-user risk in the case of saving too much money in hardware.

Scanlon says that if you're going to place five virtual machines on a single server and you're running six operating systems and all your applications, you have to work harder to deal with the situation generally, to maintain the service levels, performance, and High level. We have to invest more money than we identified during capacity planning.

According to Gordon Haff, a high-performance computing analyst at Illuminata, the detailed and accurate prediction of server performance as a virtual machine host can be complex due to the different capabilities of the chipset to support virtual workloads and hypervisors.

Haff said the virtual machine to the processor cache pressure than the physical server. The processor's ability to translate between application requirements and the hypervisor requirements is different.

Andi Mann, an analyst at the Enterprise Management Institute (EMA), said both Intel and AMD have built their circuit specifically to support virtualization and virtual server migration. A given server may be configured with two and eight processors, each with two to eight processing cores. Without a detailed and painstaking analysis, it is almost impossible to predict how different workloads of your particular server configuration can handle the software well.

If you do not study the workload you plan to put on your server, you will not be given a specific answer even if you ask your vendor's tech and sales representatives directly. Massimo Re Ferre, a senior IT designer at IBM Systems and Technology Group, said that while there are no rules to follow, some of the rules of thumb can get you closer to finding weaknesses and knowing where and how they can be strengthened. First, you can add three to five virtual machines to each core of a new Intel or AMD processor.

This is more optimized than Scanlon's vision. Scanlon said he put five or six virtual machines on a single server. If these applications are resource-intensive databases or ERP applications, he runs only two applications.

Mann said the bottom line is the better. Too much emphasis on consolidation inevitably leads to poor performance and user frustration. Re Ferre's second law of thumb is to add 2 to 4 GB of memory for each core of the new processor. This is consistent with Scanlon's assessment. He runs 48GB of memory on each of the high-end blade servers. He said that as soon as we added memory, we would not have experienced any performance problems.

Other issues that need attention:

First, do not forget to pipe work. There are many input / output requirements for having many servers. Haff said to make sure you have enough connectivity to connect to back-end storage and networking to accommodate these I / O needs.

Second, create a fence. Virtual machines are easy to launch and hard to see, so it is common for virtual machines to spread (there are too many unused virtual machines in operation). Scanlon said withdrawing all of the unused servers and the amount of hard drive space they occupy has allowed Computacenter to reclaim a lot of resources, allowing the company to postpone significant upgrades until the next budget cycle.

Third, Wolf said you have a detailed understanding of your setup with all the available tools.

VMware offers VMware's vCenter CapacityIQ 1.0 and Microsoft provides its "Assessment and Planning Toolkit for Hyper-V" tools to help guide users. However, neither of these tools is good at setting up a setup that includes VMware and Hyper-V.

Many third-party tools do include these two versions. HP itself has a tool specifically for VMware and a tool specifically for Hyper-V. Mann said those who have less to do with VMware and Microsoft can provide a more independent assessment.

These tools include Novell's PowerRecon, CiRBA, Inc's Data Center Intelligence and Akorri's BalancePoint, VKernel's Capacity Modeler. To learn more about how one customer uses CiRBA tools, see CIO.com's security study, How Underwriters Labs Cleverly Plan for Virtualization.

In the end, Re Ferre said, it is not possible to create a detailed datasheet of the host of virtual machines you are asking for and expecting. However, taking into account the time and money you need to do this yourself or pay for a professional assessment, buying more powerful hardware that exceeds your actual needs may be cheaper and you run a server at 70% capacity because It does not over-stress at 95% capacity.