Yellow Bricks

by Duncan Epping

virtual san

vSAN 6.6: Manual vs Automatic Disk Claim Mode

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I received this question on Manual vs Automatic disk claim mode in vSAN 6.6. Someone upgraded a cluster from 6.2 to 6.6 and  wanted to add a second cluster. They noticed that during the creation of the new cluster there was no option to select “automatic vs manual”.

I think a blog post will be published that explains the reasoning behind this, I figured I would share some of it before hand so you don’t end up looking for something that does not exist. In vSAN 6.6 the “Automatic” option which automatically creates disk groups for you has disappeared. The reason for this is because we see the world moving to all-flash rather fast. With All-Flash it is difficult to differentiate between the capacity and cache device. For that reason, in previous versions of vSphere/vSAN you already had to grab the devices yourself when it was an all-flash configuration. With 6.6 we removed the “automatic” option as we also recognized that when there are multiple disk groups and you need to take disk controllers, and location of disks etc in to account it even becomes more complex to automatically form disk groups. In our experience most customers preferred to maintain control and had this configured to “manual” by default. As such this option was removed.

I hope that clarifies things. I will add a link to the article explaining it.

Can I front vSAN with a VAIO Caching Solution?

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I had this question a couple of times already, so I figured I would write a quick post. In short: yes you can put a VAIO Filter in front of vSAN. The question really is, which one would you like to use and why?

First of all, the VAIO Filter needs to be certified to be placed in front of vSAN storage. Just like it needs to be certified for VMFS and NFS. You can go to the VAIO HCL and check this yourself:

In this example Infinio supports VVols, vSAN and VMFS. Great! Now the next question is: why? Well that is the bigger question, personally I don’t see a real compelling reason. For traditional storage it makes a lot of sense, as you want to keep IOs local and add cache in a “cheap way” instead of expanding, a potentially close to end of life, storage system. For vSAN that is different. vSAN has a distributed architecture and every node has a flash device that is being used for write caching, and also read caching in a hybrid scenario. If this is a new deployment invest your money in NVMe instead. If you want to repurpose existing hardware and it is not on the vSAN HCL, ask yourself if you should complicate your deployment or not?

I would personally recommend to keep it simple, but than again I can also understand you do not want to let flash resources go to waste if vSAN does not support the devices. If you want to go VAIO, make sure to check the HCL and take the potential risks and operational complexity in to account and weigh that against the cost.

vSAN Health Check fails on vMotion check

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On Slack someone asked why the vMotion check for vSAN 6.6 Health Check was failing constantly. It was easy to reproduce when using the vMotion IP Stack on your vMotion VMkernel interface. I went ahead and tested it in my lab, and indeed this was the case. I looked around and then noticed the following in the vSAN 6.6 release notes:

vMotion network connectivity test incorrectly reports ping failures
The vMotion network connectivity test (Cluster > Monitor > vSAN > Health > Network) reports ping failures if the vMotion stack is used for vMotion. The vMotion network connectivity (ping) check only supports vmknics that use the default network stack. The check fails for vmknics using the vMotion network stack. These reports do not indicate a connectivity problem.

Workaround: Configure the vmknic to use the default network stack. You can disable the vMotion ping check using RVC commands. For example: vsan.health.silent_health_check_configure -a vmotionpingsmall

I guess that clarifies things, so I figured I would test it. Here’s what it looked like before I disabled the checks:

I used RVC to disable the checks, let me show two methods:

vsan.health.silent_health_check_configure -a vmotionpingsmall /localhost/VSAN-DC/computers/VSAN-Cluster

Note that you will need to replace the “VSAN-DC/..” with your cluster and datacenter name. This disables the vMotion ping test. The other is running this command in interactive mode, that will allow you to simply enter the number of the specific test that needs to be disabled. It will list all tests for you first though.

vsan.health.silent_health_check_configure -i /localhost/VSAN-DC/computers/VSAN-Cluster

The vMotion tests are somewhere half down:

44: vMotion: Basic (unicast) connectivity check
45: vMotion: MTU check (ping with large packet size)

And of course this doesn’t only apply to the vMotion tests, with vSAN 6.6 (vCenter 6.5.0d) you can also disable any of the other tests. Just use the “interactive” mode and disable what you want / need to disable.

<UPDATE>

Note that you can now also disable health checks in the UI as shown in the GIF below. Click it to watch it!

Disk format change going from 6.x to vSAN 6.6?

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Internally I received a comment around the upgrade to 6.6 and the disk format version change. When you upgrade to 6.6 also the version of  disk changes, it goes to version 5. In the past with these on-disk format changes a data move was needed and the whole disk group would be reformat. When going from vSAN 6.2 (vSphere 6.0 U2 that is!) to vSAN 6.6 there is no data move needed. The update is simply a metadata update, and on the average cluster will take less than 20 minutes.

When introducing encryption in to the environment you will need to evac data though as this will be a reformat of the disk. Reason for it being is that the disk will need to be encrypted and so will the data. This doesn’t mean however that if you want to “rekey” your environment a full format and data move is needed, vSAN Encryption has the ability to do a so called “shallow rekey” which means that the Key Encryption Key (KEK) will be replaced (see animated gif below), but not the Data Encryption Key (DEK). It is possible to do a deep rekey, but this will mean a full reformat and data evac of all disk groups. I hope that clears things up.

Where to find the Host Client vSAN section?

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I had a couple of people asking already, so I figured I would do a short post on where to find the ESXi Host Client vSAN section. It is fairly straight forward, if you know where to click. Open the Host Client by going to https://<ip address of your host>/ui. Next do the following:

  • Click on “Storage”
  • In the right pane, click on “vSAN Datastore”
  • In the left pane, click on “Monitor”

You should now see the following:

I drew a red rectangle around the vSAN specific menu options. Just click through them. Just for demonstration purposes I disabled the VMkernel interface for vSAN on this host. As you can see in the “Hosts” section below this particular host has no “IP” address indicating you should check the network… Very useful for sure when troubleshooting.

Of, of course the Health Check and the new Config Assist option vCenter also calls this out! With a link to the object even to fix the issue. If you would click the blue link you would go to the VMkernel config section in the UI… I love it how easy it becomes to fix and detect issues. Great work vSAN team!