@cemalettin, the vsanDatastore showing 0B usable might indicate the cluster was never fully formed e.g. the nodes were not able to communicate with one another over the vSAN network (e.g. perhaps it was not configured or not configured properly).
If the disks still have vSAN partitions on them, you don't need to remove these if the Disk-Groups are intact and are usable - this is easily checked either via Cluster > Configure > vSAN > Disk Management or by running this on the node via SSH:
# vdq -Hi
If you the Disk-Group is not intact (e.g. Cache-tier has partitions wiped but Capacity-tier devices still have partitions) and you are sure you don't need any data from that Disk-Group then these can be erased via multiple means such as using 'dd' or esxcli:
# esxcli vsan storage remove -u <UUIDofDisk>
or for a Capacity-tier disk
# esxcli vsan storage remove -d <NaaofDisk>
or for a Cache-tier disk:
# esxcli vsan storage remove -s <NaaofDisk>
or from the UI: Host > Configure > Storage Devices > select the device > Erase partitions
