vSAN in fact exists perfectly well without a vCenter. vCenter is just the easy-to-use UI. However, if vCenter is lost you will need to resort to esxcli commands to be able to change vSAN settings, since the standalone html5 esxi host interface does not allow you to perform vSAN commands.
This situation has happened to me when messing around in the homelab (where my vCenters are short lived, ie, I deleted it before I disabled vSAN) or in a case where I bought homelab hardware from a friend and the vCenter didn't make the trip. Since he did provide the root password to the hosts, I was able to SSH into the host and run esxcli commands.
If disks were used by vSAN and that configuration was not properly undone, you will find that those disks cannot be re-used in a new vSAN configuration, or even to create plain datastores. I believe that information is recorded in each disk, meaning even re-installing ESXi would not clear said config.
The "delete partition" commands available through the standalone html5 interface will fail because vSAN is still running and is protecting the disks. So, before I re-install my hosts or try to re-use the storage devices, I run the below commands.
I saw other posts that achieve the same thing using fdisk and partedutil, instead of esxcli vsan commands. That would be the brute force method - below is a much simpler and safer way, that I know works in ESXi 6.5.
There's two phases.
1) The first phase is removing the host from a vSAN cluster. Check if the host believes it's in a vSAN cluster with
esxcli vsan cluster get
Remove the host from said cluster with
esxcli vsan cluster leave
This command can take a while to take effect, be patient. The host ceases collaborating with its cluster and running the get command again should show that the host is no longer a member of a vSAN cluster.
esxcli vsan cluster get
Virtual SAN Clustering is not enabled on this host
2) The second phase is clearing vSAN config from the disks so they can be re-used. Check if vSAN "owns" the disks with
esxcli vsan storage list
From the list, you want to identify the cache disk, typically the best performing SSD, and copy the device name.
Display Name: naa.50026b724712194a
Is SSD: true
Is Capacity Tier: false
The gotcha - you can't perform manual operations on vSAN disks if they were claimed automatically when vSAN was configured. You must run this command to disable that auto-claiming before proceeding (use esxcli vsan storage automode get to check if you need to do this).
esxcli vsan storage automode set --enabled false
Now enter this command with the cache device name
esxcli vsan storage remove -s naa.50026b724712194a
The -s means SSD. The command also accepts regular disks with -d. The thing to know is that doing the cache disk does all the disks in a diskgroup (ie, takes care of all capacity disks), so it's faster to just do the cache disk for the whole disk group.
This will take a while as well, but after completing, you should not see any output after issuing esxcli vsan storage list again (granted, you removed all disk groups).
I hope this helps anyone learning and playing with vSAN. Any corrections or suggestions, please reach out to me on twitter.
References to create this post (I do recommend them, they explain more):