Network Computing is part of the Informa Tech Division of Informa PLC

This site is operated by a business or businesses owned by Informa PLC and all copyright resides with them. Informa PLC's registered office is 5 Howick Place, London SW1P 1WG. Registered in England and Wales. Number 8860726.

  1. Home
  2. Data-centers
  3. Crunching-virtualization-numbers
  4. Page
  5. Crunching The Virtualization Numbers: Page 2 of 2
Data Centers

Crunching The Virtualization Numbers: Page 2 of 2

Network engineers are doing a good job of handling virtualization in their environments. Yes, you heard that right. There are some performance problems, but the adjustment from physical to virtual servers has not resulted in a large uptick in the key Layer 2 KPIs that we use to quantify LAN performance. That means that the cries from application teams about the LAN under-performing now that servers and their corresponding applications are virtualized is not based in fact. So, let's look at some
Jeremy Littlejohn
September 16, 2010

How did the virtual servers do in this comparison? Well of the 2540 interfaces that connected to multi-guest servers--meaning that we see multiple servers on a single interface--79 had output discards. That also comes to 3.11 percent. No kidding. It is exactly the same amount as the physical servers. That isn't the whole story, though.

You might assume, as I did, that because we have multiple hosts on a single interface we would see a larger amount of loss when we had it, but that is not correct either. On 79 links, we have a total of 30,518,646 output discards. Controlling for the top 95 percent, as we did with the physical servers, we have only 376,321 total drops. That number is proportional to the physical servers on a per interface basis, but the big difference is that on these 74 interfaces, we are actually hosting 463 servers. That drops our per server discards to only 812.

Even if you look only at the top 5 percent of interfaces, you get approximately the same amount of discards per interface, with the major difference being the number of VMs served by the five percent in the virtualized group. Input discards are also an issue on these server interfaces. However, we believe that input discards are tied to other factors such as shared buffer architectures. We will be looking at them over the next week to let you know if the data backs up that hypothesis. In the meantime, let's track down these bad interfaces, virtual or not, and fix them.

Tags:

Commentary
Data Centers