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Now that you have been introduced to the vSphere Storage Appliance (VSA), lets have a look at some of its cool features. Firstly you should be aware that the VSA can handle failures at both the ESXi host and appliance level, and continue to present the full complement of NFS datastores. This means that if the ESXi host on which the appliance is running goes down, the cluster will seamlessly present that NFS datastore from another node in the cluster. This is transparent to the ESXi servers that have the NFS datastore mounted, and is thus transparent to any VMs running on that datastore.

Let's discuss what happens if you have a hardware failure on one of your ESXi hosts, and the server vendor is going to take a while to ship you the replacement part. One of the cool features of the VSA is that it will allow you to replace an offline/failed node with a brand new ESXi host. Look at my 2 node configuration here:

In this case, I have lost one of the nodes in my two node cluster (and of course the appliance VSA-0 running on that node). In this case, VSA-1 will take over the presentation of the NFS datastore from VSA-0. This places both of the NFS datastores into a degraded state, but of course the datastores are still presented to the ESXi hosts and the VMs on those datastores are unaffected and continue to run. Degraded here means that they have no mirror copy/replica. The only issue is that both NFS datastores are now being presented from the same appliance on the same ESXi host, so if I have another issue while waiting for the replacement part, I'm goosed. The VSA Manager will show the appliance as offline in the Appliances view in VSA Manager:

To replace this node with a brand new node, and bring the cluster out of the degraded state, simply select the offline appliance, right click on it, & select the option to do a 'Replace Appliance':

Now it is simply a matter of following the wizard driven steps to replace the offline appliance with a new appliance on a new ESXi server. Just like the installation process, the UI will show you all available ESXi 5.0 hosts in the datacenter. Obviously two of these hosts are already used by the VSA cluster (one of which is failed), and are not available for selection, but in the example below I have a third host that is not in the cluster which can be used:

When the networking has been configured on the replacement ESXi & the VSA appliance deployed (all of which is done automatically), the volume & replica are created on the new appliance and synchronized with the NFS volumes already in the VSA cluster. When all this is completed, the Replace Appliance wizard will display the following:

The VSA cluster is now back to its optimal state. So even though a node in the VSA cluster may suffer a hardware failure, procedures have been built into the VSA cluster to help customers keep it highly available, allowing a failed node to be swapped out of the cluster for a new healthy server. And this can be done while the VSA cluster continues to present a full complement of NFS datastores. I'm sure you will agree that this is a very nice feature of the vSphere Storage Appliance. Now you just have to wait for that replacement part to turn up! 🙂

About the Author

Cormac Hogan

Cormac Hogan is a Senior Staff Engineer in the Office of the CTO in the Storage and Availability Business Unit (SABU) at VMware. He has been with VMware since April 2005 and has previously held roles in VMware’s Technical Marketing and Technical Support organizations. He has written a number of storage related white papers and have given numerous presentations on storage best practices and vSphere storage features. He is also the co-author of the “Essential Virtual SAN” book published by VMware Press.