VMware: vSAN 6.6 not showing all available disks when attempting to claim...

Summary:
Was going through and attempting to setup new vSAN cluster but noticed that the wizard was only showing 3 of 4 disks from 3 of 4 hosts and 0 disks from another host.  This appears to be by design where the setup wizard will only target disks that have 0 partitions.  Makes sense.

This, however, is not obvious in the setup.

Solution:
Simply delete any partitions from those disks that you'd like to have vSAN claim.  You can do this enmasse via PowerCLI or the Web Client interface (as pictured below).
[Warning: This is a destructive process so be sure that you know absolutely for certain that you are targeting the correct storage devices.  This is especially true if you plan to script this process.]

Erase Partition in Web Client

The above process would suck if you were doing it against a large cluster, so learn to do it in powershell or some other automated method.

PowerCLI Method:

$TCluster = Get-Cluster TargetClusterName
$TVMHosts = $TCluster | Get-VMHost | Get-View
Foreach ($VMHost in $TVMHosts)
{
    $ConfigManager = Get-View $VMHost.ConfigManager.StorageSystem
    #Spec defined and left blank to clear partitions
    $Spec = New-Object vmware.vim.hostdiskpartitionspec
    #I'm simply targeting all naa devices and those that state local disk. 
    #Reality is that you'd probably want a more in depth filter on the devices you target. 
    #My case was a new set of hosts, so this worked for me.
    $TargetDisks = $VMHost.config.StorageDevice.scsilun | Where {$_.DevicePath -match "naa." -and $_.LocalDisk -eq "true"}
    Foreach ($Disk in $TargetDisks)
    {
        $ConfigManager.UpdateDiskPartitions($Disk.DevicePath, $Spec)
    }
}

Side Note:
vSAN claimed disks have a protection mechanism against being erased via above defined method.  Any partitions that it runs into claimed by vSAN will be met w/ an exception of "Cannot change the host configuration"
If you for some reason need to delete those partitions, then you'll like have to try this method:

vSAN: Rebuilding an ESXi host that has vSAN claimed disks...