Does more NICs on a server mean potential for more sustained concurrent I/O?

Question

If you're trying to build an application that needs to have the highest possible sustained network bandwidth, for multiple and repetitive file transfers (not for streaming media), will having 2 or more NICs be beneficial?

Answer 1

It can be beneficial, but it won't necessarily be that way "out of the box".

You need to make sure that both NICs actually get used - by separating your clients on different network segments, by using round robin DNS, by using channel bonding, by using a load balancer, etc. And on top of that you need to make sure your network infrastructure actually has sufficient bandwidth to allow more throughput.

But the general principle is sound - you have less network bandwidth available on your server than disk I/O, so the more network bandwidth you add the better, up until it reaches or exceeds your disk I/O, then it doesn't help you anymore.

Answer 2

Potentially yes. In practice, it also depends on the network fabric, and whether or not network I/O is a bottleneck for your application(s).

Answer 3

I think your answer will depend on your server and network architecture, and unfortunately may change as they change.

What you are essentially doing is trying to remove the 'current' bottleneck in your overall application or design which you have presumably identified as your current NIC (if you haven't actually confirmed this then I would stop and check this in case something else restricts throughput before you reach your NIC limit).

Some general points on this type of performance optimization:

• It is worth checking if you have the option to upgrade the current NIC to a higher bandwidth interface - this may be a simpler solution for you if it avoids having to add load balancing hardware/software/configuration to your application.

• As pointed out above you need to make sure all the other elements in your network can handle this increased traffic - i.e. that you are not simply going to have congestion in your internet connection or in one of your routers

• Similarly, it is worth checking what the next bottle neck will be once you have made this change, if the traffic continues to increase. If adding a new NIC only gives you 5% more throughput before you need a new server anyway, then it may be cheaper to look for a new server right away with better IO from new.

• the profile of your traffic and how it is predicted to evolve may influence your decision. If you have a regular daily peak which only exceeds your load slightly then a simple fix may serve you for a long time. If you have steadily growing traffic then a more fundamental look at your system architecture will probably be necessary.

• In line with the last point above, it may be worth looking at the various Cloud offerings to see if any meet your requirements at a reasonable cost, possibly even as temporary resource every day just to get you through your peak traffic times.

And finally you should be aware that as soon as you settle on a solution and get it up and running someone else in your organization will change or upgrade the application to introduce a new and unexpected bottle-neck...