This note is, again, for me to remind myself in case I couldn’t recall how to do this in the future.

To remove a storage domain from the cluster, use the following steps:

  1. Click Storage -> Domains
  2. Click on the name of the storage domain to open the details view
  3. Click on the Data Center tab
  4. Click on Maintenance button, then click on OK
  5. The Detach button becomes active, click on it.
  6. Click on Remove

Reference: