Resize-StorageTier / Expand Volume on Windows Server 2025 Campus Cluster does not work

The pool’s raw free capacity is not the same as capacity that a Storage Spaces tier can extend. Resiliency, column count, fault domains, and the distribution of free extents can leave space visible in the pool but unusable by that tier. First confirm that the pool, virtual disk, physical disks, and storage jobs are healthy. Run Get-StorageTierSupportedSize for the exact tier and treat its reported maximum as the expandable size. If it has not increased, verify that new drives are eligible, balanced across required fault domains, and compatible with the tier’s media type. Allow optimization or rebalancing to finish before retrying. When supported space becomes available, resize the storage tier first, then the virtual disk, and finally the partition. Avoid forcing a size from the pool total. If supported size remains unchanged after healthy rebalancing, collect cluster and Storage Spaces health data before treating this as a Server 2025 defect