The Virtualization Room

Sep 23 2008   4:10AM GMT

Using blades as virtual hosts

Eric Siebert Eric Siebert Profile: Eric Siebert

Blades have come a long way since the early days of very few options and limited expandability. Most early blade servers only had one or two NICs, limited storage, no Fibre Channel support, and limited CPU and memory, which made them poor choices for virtual hosts. That’s all changed in recent years as blade technology has evolved and no longer has the limitations of earlier blades, making them ideal for virtual host servers. Modern blade servers can support up to 16 NICs, four quad-core processors and multiple Fibre Channel or iSCSI HBA adapters. When considering blade servers in your environment as an alternative to traditional rack mount servers, you need to know the advantages and disadvantages of each and why you might choose one type over another.

Some reasons you might choose blade servers over traditional servers:

  • Rack density is better for data centers where space is a concern. Up to 50% more servers can be installed in a standard 42U rack compared with traditional servers.
  • Blade servers provide easier cable management as they simply connect to a chassis and need no additional cable connections.
  • Blade servers have lower power consumption than traditional servers because of reduced power and cooling requirements.
  • Blade servers can be cheaper than traditional servers when comparing a fully populated chassis with the equivalent number of traditional servers.

Some reasons you might choose traditional servers over blade servers:

  • Traditional servers have more internal capacity for local disk storage. Blade servers typically have limited local disk storage capacity due to the limited drive bays. Some blade vendors now have separate storage blades to expand blade storage, but this takes up additional slots in the blade chassis.
  • Traditional servers have more expansion slots available for network and storage adapters. Blade servers typically have very few or no expansion slots. Virtual hosts are often configured with many NICs to support the console network, vmKernel network, network-attached storage and virtual machine networks. Additional network adapters are also needed to provide failover and load balancing.
  • Once a chassis is full, purchasing a new chassis to add a single new additional server can be costly. Traditional servers can be installed without any additional infrastructure components.
  • Traditional servers are often less complicated to set up and manage than blade servers.
  • Traditional servers have multiple USB ports for connecting external devices and also an optical drive for loading software on the host. They also have serial and parallel ports, which are sometimes used for hardware dongles for licensing software. Additionally, tape backup devices can be installed in them. Blade servers make use of virtual devices that are managed through the embedded hardware management interfaces.

Many people that use blade servers as virtual hosts often take advantage of the boot-from-SAN feature so they don’t need internal storage on their blade servers. The choice between blade and traditional servers often comes down to personal preference and what type of server is already in use in your data center. Some people like blades, others don’t. Regardless of which server type you choose, they both work equally well as virtual hosts.

2  Comments on this Post

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  • Rick Vanover
    I am convinced blades as hosts is a great solution for very large virtual environments in terms of number of hosts. They are also good in space constrained situations of course. Another strategy is to mix blades - meaning within a chassis, have a few virtual host, a big database server, and the email server.
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  • Slowe
    Another reason organizations may not adopt blades is strictly a facilities issue--the higher rack density that blades create also requires a much higher power density and a much higher cooling density as well. Some data centers may have enough power overall, but can't deliver that much power to that one spot. Similarly, data centers may be able to keep a rack full of traditional rack-mounted servers cool, but would not be able to keep a rack full of blades cool.
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