1) Filer model? 2) Ontap version? 3) Block storage? a)Do you know which Data Aggregate is hosting the 'Datastore(Virtual Machines)' volume? b)Data Aggregate 'size/used/available' in gb/tb? 4) Is the Volume inside the Data Aggregate : Thick or Thin?
I see...this is a 'VMware/SolidFire' configurations. I googled the error you mentioned 'blockClusterFull', this term is not used in FAS terminology. It seems you have a 'SolidFIre NetApp Storage'. Is that correct ?
Note: All datastores on SolidFire are thin provisioned so if a volume is reported as being "more full" in SolidFire than in ESX even after deleting a VMs, then unmap will help. The vmfs unmap command is an online operation that can be run with the datastore mounted and in use by VMs. It can be started from command line 'esxcli 'or from the SolidFire VCP plugin.
From screenshot, it appears there is enough space on Datastore, so i believe unamp should help free blocks on the storage side. Follow the kb and let us know. As a side note: If unmap does not help much, check the number of snapshots on your cluster side and try delete the oldest one that you can get rid of, and see if it frees up space (Have no idea how GUI looks, as I am not a familiar with SolidFire).