I was recently helping out my friend Paudie O'Riordan with a request from a customer who was looking for a way to collect detailed space utilization for their VMs (VM Home, VMDK & swap) running on VSAN. Today, this level of granularity is not available in the vSphere UI and the customer was interested in both the used and reserved capacity on a per-VM basis. Luckily, this information can be retrieved using the VSAN Management API.
To do so, we just need to use the VsanQueryObjectIdentities() API method, which I have used in the past to retrieve things like "thick" provisioned VM and translating VSAN Object IDs to their friendly VM display name. To retrieve space utilization information, we just need to set the includeSpaceSummary property to be true. While developing the PowerCLI sample script, I found that this specific property is currently not supported when querying vCenter Server and to retrieve this information, you must go directly to each ESXi host within the VSAN Cluster. I have already filed a feature request and it looks like this will be fixed in a future vSphere release.