Yellow Bricks

by Duncan Epping

u2

vSAN Storage Rules policy capability allows to set dedupe per VM?

· · 4 Comments

There was a question posted on the VMware Community Forums, and as this is something I have been asked regularly, I figured I would do a quick blog post about it. Although I have covered this before, it doesn’t hurt to repeat, as it appears to be somewhat confusing for people. When you create a VM Storage Policy, starting with vSAN 7.0 U2 you have the ability to specify if a VM needs to be Encrypted, have Dedupe and Compression enabled, have Compression-Only enabled, and/or needs to be stored on all-flash vSAN or Hybrid. Never noticed it? Look at the screenshot below.

In the screenshot, you see that you have the ability to specify which data service needs to be enabled. I guess this is where the confusion comes into play, as this functionality is not about enabling the data service for the VM to which you assign the policy. This is about which data service needs to be enabled on the datastore to which the VM can be provisioned. Huh, what? Okay, let’s explain.

If you are using vSAN as your storage platform, and you are sharing vSAN Datastores between clusters leveraging the HCI Mesh feature, then you could find yourself in a situation where some clusters are hybrid and some are all-flash. Some may have data services enabled like Encryption or Deduplication, some may not. In that scenario you want to be able to specify which features need to be enabled for the datastore the VM is provisioned to. So what this “storage rules” feature does is that it ensure that the datastore which is shown as “compatible” actually has the specified capabilities enabled! In other words, if you tick “data-at-rest encryption” in a policy and assign the policy to a VM, then only the datastores which have “data-at-rest encryption” enabled will be shown as compatible with your VM!

So again, “storage rules” apply to the data services that should be enabled on the vSAN Datastore, and do not enable data services on a per VM/VMDK basis.

Which vSAN Maintenance Mode option was used on a host?

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Last week there was a question on VMTN around maintenance mode, this customer wanted to find out which vSAN Maintenance Mode option was used while the host was placed in maintenance mode. The person who placed the host into maintenance wasn’t around, and I guess the customer wanted to know if data was moved from the host or not. They looked at the events and tasks, but unfortunately it wasn’t obvious from that vCenter section, next up were the logs. I also looked at the logs, and you would expect this info to be stored in hostd.log, but it wasn’t, so where is it? Well it actually is a configuration item, and you can dig it up here:

Pre ESXi 7.0 the info is stored in the “esx.conf” file, just grep for “hostDecommission”. Let me show you:

$ grep "/vsan/hostDecommission" /etc/vmware/esx.conf
/vsan/hostDecommissionVersion = "10"
/vsan/hostDecommissionState = "decom-state-decommissioned"
/vsan/hostDecommissionMode = "decom-mode-ensure-object-accessibility"

If the ESX is at 7.0 or later, just run the below config store command:

$ configstorecli config current get -c vsan -g system -k host_state
{
   "decom_mode": "ENSUREOBJECT_ACCESSIBILITY",
   "decom_state": "DECOMMISSIONED",
   "decom_version": 0
}

I hope that helps others who have a similar question!

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

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.

Site locality in a vSAN Stretched Cluster?

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On the community forums, a question was asked around the use of site locality in a vSAN Stretched Cluster. When you create a stretched cluster in vSAN you can define within a policy how the data needs to be protected. Do you want to replicate across datacenters? Do you want to protect the “site local data” with  RAID-1 or RAID-5/6? All of these options are available within the UI.

What if you decide to not stretch your object across locations, is it mandatory to specify which datacenter the object should reside in?

The answer is simple: no it is not. The real question, of course is, would be: should you define the location? Most definitely! If you wonder how to do this, simplicy specify it within the policy you define for these objects as follows:

The above screenshot is taken from the H5 client, if you are still using the Web Client it probably looks slightly different (Thanks Seamus for the screenshot):

Why would you do this? Well, that is easy to explain. When the objects of a VM get provisioned the decision will be made per object where to place it. If you have multiple disks, and you haven’t specified the location, you could find yourself in the situation where disks of a single non-stretched VM are located in different datacenters. This is, first of all, terrible for performance, but maybe more importantly also would impact availability when anything happens to the network between the datacenters. So when you use site locality for non-stretched VMs, make sure to also configure the location so that your VM and objects will align as demonstrated in the below diagram.