Yellow Bricks

by Duncan Epping

HCI Mesh error: Failed to run the remote datastore mount pre-checks

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I had two comments on my HCI Mesh compute only blogpost where both were reporting the same error when trying to mount a remote datastore. The error that popped up was the following:

Failed to run the remote datastore mount pre-checks.

I tried to reproduce it in my lab, as both had upgraded from 7.0 to U2 I did the same, that didn’t result in the same error though. The error doesn’t provide any details around why the pre-check fails, as shown below in the screenshot. After some digging I found out that the solution is simple though, you need to make sure IPv6 is enabled on your hosts. Yes, even when you are not using IPv6, it still needs to be enabled to pass the pre-checks. Thanks, Jiří and Reza for raising the issue!

HCI Mesh error: Failed to run the remote datastore mount pre-checks

Can 2-node or Stretched be used as client or server cluster with vSAN HCI Mesh?

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I had this question today, probably sparked by my post earlier where a showed a single-node cluster being able to leverage HCI Mesh to mount a remote vSAN Datastore. The question was if this also works with 2-node vSAN or with a vSAN Stretched Cluster. Unfortunately, the answer is no, a 2-node cluster or a vSAN Stretched Cluster is not supported with HCI Mesh today. Yes, this is a hard limit today, meaning that the “health check”, which is done before mounting the datastore, will actually report the issue and not allow it to progress. You can imagine that this is the result of the latency and bandwidth/throughput requirements there are in place for vSAN HCI Mesh today. This may, or may not, change over time.

Does vSAN Enhanced Durability work when you have a limited number of hosts?

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Last week I had a question about how vSAN Enhanced Durability works when you have a limited number of hosts. In this case, the customer had a 3+3+1 stretched cluster configuration, and they wondered what would happen when they would place a host into maintenance mode. Although I was pretty sure I knew what would happen, I figured I would test it in the lab anyway. Let’s start with a high-level diagram of what the environment looks like. Note I use a single VM as an example, just to keep the scenario easy to follow.

In the diagram, we see a virtual disk that is configured to be stretched across locations, and protected by RAID-1 within each location. As a result, you will have two RAID-1 trees each with two components and a witness, and of course, you would have a witness component in the witness location. Now the question is, what happens when you place esxi-host-1 into maintenance mode? In this scenario, vSAN Enhanced Durability will want to create a “durability component”. This durability component is used to commit all new write IO to. This will allow vSAN to resync fast after maintenance mode, and enhances durability as we would still have 2 copies of the (new) data.

However, in the scenario above we only have 3 hosts per location. The question then is, where is this delta component created then? As normally with maintenance mode you would need a 4th host to move data to. Well, it is simple, in this case, what vSAN does is it creates a “durability component” on the host where the witness resides, within the location of course. Let me show you in a diagram, as that makes it clear instantly.

By adding the Durability component next to the witness on esxi-host-3, vSAN enhances durability even in this stretched cluster situation, as it provides a local additional copy of new writes. Now, of course I tested this in my lab. So for those who prefer to see a demo, check out the youtube video below.

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?