2 Node vSAN Design for a Remote Site

I was recently asked to design a solution for a remote site.  The requirements were it had to be cheap, run a few virtual machines, fail over capability and have shared storage The workloads are going to be very light so there is no need for powerful servers.  I had a few options with this.  Technically one server could run the entire workload, but that does not allow for any failure so I needed at least two servers.  This would provide a fail over capacity of only 1.  Bare minimum but acceptable for this use case.  These two servers would need some kind of shared storage. One option would be using a small storage array such as the DELEMC VNXe.  I have used these previously, and they were a great solution for the time, but the times are changing and I think hyperconvergence is the future.  With vSAN 6.5 there were a lot of new features that it would make it a perfect solution.

Previously with any Hyperconvereged solution you needed 3 nodes.  3 nodes are used to check for everything being online.  If 1 out of the 3 nodes goes down the other two nodes can check with each other to verify that the node actually went down.  To get away with using 2 nodes you use an external witness.  This external witness could run on a separate server on the site or at the main data center.

With vSAN you have one SSD per Disk Group (DG) to be used for cache.  Since this had to be a cheap solution my area on constraint was cost, and everything had to be a minimal design to get the job done.  Each server would have 1 DG with an 800GB SSD and 4 4TB 7.2k HHD.  This allowed for FTT=1 or only 1 host could be lost.  There is some risk with this design.  There is always a chance that in a maintenance situation one of the host would be in maintenance mode, and  this would leave a single point of failure.  Because there would only be 1 DG available on the one online host, but this is an acceptable risk for the constraint of cost.

One of my favorite new features with 6.5 is direct connect.  With this you can now directly connect two hosts to each other instead of running through a switch.  Each of these server have 2 1GB ports and 2 10GB ports. The remote site switch infrastructure is only 1GB.  Now 1GB can be a serious limitation for storage, and I wanted to avoid that.  With direct connect you can directly connect the two host to each other, and all storage traffic would then go across that link.  Leaving the 1GB ports to be used by the VM traffic.

As you can tell this is an bare minimum design for vSAN and hyperconvergence.  It does meet all the requirements such as Cost, Availability, Share Storage.  In the event of a host going down HA can restart all the VM’s on the second node providing minimal downtime.  This provides the optimal solution for the requirements of the design.


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