Yellow Bricks

by Duncan Epping

Using HCI Mesh with a stand-alone vSphere host?

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Last week at the French VMUG we received a great question. The question was whether you can use HCI Mesh (datastore sharing) with a stand-alone vSphere Host. The answer is simple, no you cannot. VMware does not support enabling vSAN, and HCI Mesh, on a single stand-alone host. However, if you still want to mount a vSAN Datastore from a single vSphere host, there is a way around this limitation.

First, let’s list the requirements:

  1. The host needs to be managed by the same vCenter Server as the vSAN Cluster
  2. The host needs to be under the same virtual datacenter as the vSAN Cluster
  3. Low latency, high bandwidth connection between the host and the vSAN Cluster

If you meet these requirements, then what you can do to mount the vSAN Datastore to a single host is the following:

  1. Create a cluster without any services enabled
  2. Add the stand-alone host to the cluster
  3. Enable vSAN, select “vSAN HCI Mesh Compute Cluster”
  4. Mount the datastore

Note, when you create a cluster and add a host, vCenter/EAM will try to provision the vCLS VM. Of course this VM is not really needed as HA and DRS are not useful with a single host cluster. So what you can do is enable “retreat mode”. For those who don’t know how to do this, or those who want to know more about vCLS, read this article.

As I had to test the above in my lab, I also created a short video demonstrating the workflow, watch it below.

vSphere Native Key Provider backup not working

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I had three people asking this question the past few weeks, they were trying to configure the vSphere Native Key Provider so that they could enable vSAN Encryption, but the backup function wasn’t working. If you have not seen the Native Key Provider in action yet, just watch the video below.

As demonstrated in the video, when you configure the vSphere Native Key provider, you need to back up the key first before you can use it. Now, as mentioned, I had a few folks asking the past weeks why they couldn’t back up the key. The reason for it is simple, when you configure the Native Key Provider and want to back it up, you need to access the vSphere UI via the fully qualified domain name. In other words, when you access the H5 UI via the IP address of the vCenter Server, then the backup function won’t work. Also, when you have multiple vCenter Server instances in Linked Mode, you need to make sure you access the correct vCenter Server, the vCenter Server instance on which the Native Key Provider is enabled. Isn’t all of this documented? Yes, it is! But who reads documentation these days right?

vSAN File Services and Stretched Clusters!

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As most of you probably know, vSAN File Services is not supported on a stretched cluster with vSAN 7.0 or 7.0U1. However, starting with vSAN 7.0 U2 we now fully support the use of vSAN File Services on a stretched cluster configuration! Why is that?

In 7.0 U2, you now have the ability to specify during configuration of vSAN File Services to which site certain IP addresses belong. In other words, you can specify the “site affinity” of your File Service services. This is shown in the screenshot below. Now I do want to note, this is a soft affinity rule. Meaning that if hosts, or VMs, fail on which these file services containers are running it could be that the container is restarted in the opposite location. Again, a soft rule, not a hard rule!

Of course, that is not the end of the story. You also need to be able to specify for each share with which location they have affinity. Again, you can do this during configuration (or edit it afterward if desired), and this basically then sets the affinity for the file share to a location. Or said differently, it will ensure that when you connect to file share, one of the file servers in the specified site will be used. Again, this is a soft rule, meaning that if none of the file servers are available on that site, you will still be able to use vSAN File Services,  just not with the optimized data path you defined.

Hopefully, that gives a quick overview of how you can use vSAN File Services in combination with a vSAN Stretched Cluster.  I created a video to demonstrate these new capabilities, you can watch it below.

vSAN 7.0 U2 now integrates with vSphere DRS

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One of the features our team requested a while back was integration between DRS and vSAN. The key use case we had was for stretched clusters. Especially in scenarios where a failure has occurred, it would be useful if DRS would understand what vSAN is doing. What do I mean by that?

Today when customers create a stretched cluster they have two locations. Using vSAN terminology these locations are referred to as the Preferred Fault Domain and the Secondary Fault Domain. Typically when VMs are then deployed, customers will create VM-to-Host Affinity Rules which state that VMs should reside in a particular location. When these rules are created DRS will do its best to ensure that the defined rule is adhered to. What is the problem?

Well if you are running a stretched cluster and let’s say one of the sites go down, then what happens when the failed location returns for duty is the following:

  • vSAN detects the missing components are available again
  • vSAN will start the resynchronization of the components
  • DRS runs every minute and rebalances and will move VMs based on the DRS rules

This means that the VMs for which rules are defined will move back to their respective location, even though vSAN is potentially still resynchronizing the data. First of all, the migration will interfere with the replication traffic. Secondly, for as long as the resync has not completed, I/O will across the network between the two locations, this will not only interfere with resync traffic, it will also increase latency for those workloads. So, how does vSAN 7.0 U2 solve this?

Starting with vSAN 7.0 U2 and vSphere 7.0 U2 we now have DRS and vSAN communicating. DRS will verify with vSAN what the state is of the environment, and it will not migrate the VMs back as long the VMs are healthy again. When the VMs are healthy and the resync has completed, you will see the rules being applied and the VMs automatically migrate back (when DRS is configured to Fully Automated that is).

I can’t really show it with a screenshot or anything, as this is a change in the vSAN/DRS architecture, but to make sure it worked I recorded a quick demo which I published through Youtube. Make sure to watch the video!

vSAN 7.0 U2 Durability Components?

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Last week I published a new demo on my youtube channel (at the bottom of this post) and it discussed an enhanced feature called Durability Components. Some may know these as “delta components” as well. These durability components were introduced in vSAN 7.0 Update 1 and provided a mechanism to maintain the required availability for VMs while doing maintenance. That meaning that when you would place a host into maintenance mode new “durability components” would be created for the components which were stored on that host. This would then allow all the new VM I/O to be committed to the existing component, as well as the durability component.

Now, starting with vSAN 7.0 Update 2, vSAN also uses these durability components in situations where a host failure has occurred. So if a host has failed, durability components will be created to ensure we still maintain the specified availability level specified within the policy as shown in the diagram above. The great thing is that if a second host fails in an FTT=1 scenario and you are able to recover the first failed host, we can still merge the data with the first failed host with the durability component! So not only are these durability components great for improving the resync times, but they also provide a higher level of availability to vSAN! To summarize:

  1. Host fails
  2. Durability components are created for all impacted objects
  3. New writes are committed to existing components and the new durability components
  4. Host recovers
  5. Durability components are merged with the previously failed components
  6. Durability components are deleted when resync has completed

I hope that help providing a better understanding of how these durability components help improving availability/resiliency in your environment with vSAN 7.0 Update 2.

I can understand that some of you may not want to test durability components in their own environment, this is why I recorded a quick demo and published it on my youtube channel. Check out the video below, as it also shows you how durability components are represented in the UI.