Thinking about Data Center Solutions

Engineers from La Salle-URL share the latest news and projects in the field of network solutions in telematic engineering.

26 April 2016 | Posted by Redacción Data Center

Quality of Service

Hey folks! How you doing?

A long time ago since we post our last news about datacenters. We already know you have been missing us, but we are back! Prepare your chair, your soft-drink and let's start!

On our today's post we are going to introduce another interesting topic, Quality of Service. 

Why quality of service?

Because is very important depending on which kind of traffic is going to cross our network and how is gonna be managed. Is not the same a video streaming traffic than a typical backup of files. Is very important to have priorities in order to avoid some problems of transmission, like delays, lossing quality of image, interruption during the streaming, and so on. As you can see Quality of Service is very important.

An accurate definition of QoS will be: "A set of technologies for managing network traffic in a cost-effective manner to enhance user experiences for home and enterprise environments. Besides, allow the measure of bandwidth, detect changing network conditions (such as congestion or availability of bandwidth), and prioritize or throttle traffic."

So, now that that we have a better idea, is time to talk about QoS in a datacenter.

First thing that we need to take into account is that there is more than one way to provide QoS in a datacenter. Here are four different ways of deployment:

  • Hypervisor QoS: As the own tittle says, the Hypervisor stands for this function. Most hypervisors can do QoS, such as the vSwitch in VMware’s ESX.
  • Adapter-based QoS with hardware protocol offload: Moving the switching functions from the hypervisor to the adapter offers not only minimum bandwidth guaranteed QoS, but hardware offload capabilities, which lower the server RAM and CPU utilization and maximize overall system performance. QLogic technology for switch-agnostic NIC Partitioning (NPAR) dedicates bandwidth and QOS specifically to individual applications, such as VM mobility, hypervisor management or storage traffic, along with the various applications running in the VMs that are being serviced. One of the primary use cases for 10GbE is as a replacement for multiple GbE NIC cards to support just these types of services. All processing related to switching, including VM-to-VM communication without an external switch, is handled on the adapter rather than on the server, thus dedicating server resources (RAM and CPU) to applications and not to network protocol processing and QoS. NPAR operates independently from the network infrastructure.
  • Adapter-based QoS with software initiators: In this case the NIC handles the QoS, but the protocol processing is still performed in software running on the CPU, which affects the CPU’s overall performance.
  • Rate limiting: Some QoS implementations only support a simple rate limiting paradigm, rather than intelligent QoS with a minimum bandwidth guarantee. With rate limiting, each application is assigned a specific amount of bandwidth that cannot be exceeded, regardless of whether the bandwidth assigned to other applications is being used. This approach limits flexibility and can result in stranded bandwidth throughout the day when that bandwidth could have been put to use improving the performance of the applications.

In order to use or deploy QoS in a datacenter is important to have in mind these features:

  • Adapter-based QoS with hardware protocol offloads to avoid using server CPU and RAM resources.
  • The ability to assign applications to virtual connections with a guaranteed amount of bandwidth.
  • The ability to allow applications to burst above their guaranteed amount if extra bandwidth is available.

Benefits and drawbacks of QoS in a datacenter

We have explained a little bit about QoS in a datacenter, but which benefits or drawbacks could bring to us?

Benefits:

  • Capability of prioritize traffic: This means allowing first the most important flows and then the less important flows.
  • Better reliability in the network.

Drawbacks:

  • If we priorize some traffic than other, sometimes we will obtain a poor perfomance for these applications.

 

Hope this post has been useful for you. See you next weeek!

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