virtual san

Since I started playing with Virtual SAN there was something that I more or less avoided / neglected and that is Network IO Control. However, Virtual SAN and Network IO Control should go hand-in-hand. (And as such the Distributed Switch.) Note that when using VSAN (beta) the Distributed Switch and Network IO Control come with it. I guess I skipped it as there were more exciting thing to talk about, but as more and more people are asking about it I figured it is time to discuss Virtual SAN and Network IO Control. Before we get started, lets list the type of networks we will have within the VSAN cluster:

• Management Network
• vMotion Network
• Virtual SAN Network
• Virtual Machine Network

Considering it is recommend to use 10GbE with Virtual SAN that is what I will assume with this blog post. In most of these cases, at least I would hope, there will be a form of redundancy and as such we will have 2 x 10GbE to our disposal. So how would I recommend to configure the network?

Lets start with the various portgroups and VMkernel interfaces:

• 1 x Management Network VMkernel interface
• 1 x vMotion VMkernel interface (All interfaces need to be in the same subnet)
• 1 x Virtual SAN VMkernel interface
• 1 x Virtual Machine Portgroup

Some of you might be surprised that I have only listed the vMotion VMkernel interface and the Virtual SAN VMkernel interface once… And after various discussions and thinking about this for those I figured I would keep things as simple as possible, especially considering the average IO profile of server environments.

By default we can make sure the various traffic types are separated on different physical ports, but we can also set limits and shares when desired. I do not recommend using limits though, why limit a traffic type when you can use shares and “artificially limit” your traffic types based on resource usage and demand?! Also note that shares and limits are enforced per uplink.

So we will be using shares, as shares only come in to play when there is contention. What we will do is take 20GbE in to account and carve it up. Easiest way, if you ask me, is to say each traffic type gets an X number of GbE assigned at a minimum which is based on some of the recommendations out there for these types of traffic:

• Management Network –> 1GbE
• vMotion VMK –> 5GbE
• Virtual Machine PG –> 2GbE
• Virtual SAN VMkernel interface –> 10GbE

Now as you can see “management”, “virtual machine” and vMotion” traffic share Port 1 and “Virtual SAN” traffic uses Port 2. This way we have sufficient bandwidth for all the various types of traffic in a normal state. We also want to make sure that no traffic type can push out other types of traffic, for that we will use the Network IO Control shares mechanism.

Now lets look at it from a shares perspective.You will want to make sure that for instance vMotion and Virtual SAN always has sufficient bandwidth. I will work under the assumption that I only have 1 physical port available and all traffic types share the same physical port. We know this is not the case, but lets take a “worst case scenario” approach.

Lets assume you have a 1000 shares in total and lets take a worst case scenario in to account where 1 physical 10GbE ports has failed and only 1 is used for all traffic. By taking this approach you ensure that Virtual SAN always has 50% of the bandwidth to its disposal while leaving the remaining traffic types with sufficients bandwidth to avoid a potential self-inflicted DoS.

You can imagine that when you select the uplinks used for the various types of traffic in a smart way that even more bandwidth can be leveraged by the various traffic types. After giving it some thought, this is what I would recommend per traffic type:

• Management Network VMkernel interface = Explicit Fail-over order = P1 active / P2 standby
• vMotion VMkernel interface = Explicit Fail-over order = P1 active / P2 standby
• Virtual Machine Portgroup = Explicit Fail-over order = P1 active / P2 standby
• Virtual SAN VMkernel interface = Explicit Fail-over order = P2 active / P1 standby

Why use Explicit Fail-over order for these types? The best explanation here is predictability. By separating traffic types we allow for optimal storage performance while also providing vMotion and virtual machine traffic sufficient bandwidth.

Also vMotion traffic is bursty and can / will consume all available bandwidth, so when combined with Virtual SAN on the same uplink you could see how these two could potentially hurt each other. Of course depending on the IO profile of your virtual machines and the type of operations being done. But you can see how a vMotion of a virtual machine provisioned with a lot of memory can impact the available bandwidth for other traffic types. Don’t ignore this, use Network IO Control!

Lets try to visualize things, makes it easier to digest. Just to be clear, dotted lines are “standby” and the others are “active”.

I hope this provides some guidance around how to configure Virtual SAN and Network IO Control in a VSAN environment. Of course there are various ways of doing it, this is my recommendation and my attempt to keep things simple and based on experience with the products.