An administrator is trying to add a new virtual disk of 3TB to a virtual machine on a recently upgraded ESXi 6.x host, but receives this error: The disk capacity entered was not a properly formed numb

Upgrading the VMFS datastore version (e.g., from VMFS3 to VMFS5) does not retroactively reconfigure the block size on the existing volume; the block size must be set explicitly before the large disk can be created.

VMFS3 datastores use configurable block sizes (1MB, 2MB, 4MB, or 8MB), where the default 1MB block size limits the maximum virtual disk file to approximately 256GB. Changing the block size to 8MB increases the maximum supported virtual disk size to approximately 2TB, resolving the out-of-range error that appears when attempting to provision oversized disks on datastores with undersized block configurations.

The error is not caused by insufficient free space but by a block size constraint, so moving the VM to a different datastore does not resolve it unless that datastore also has the correct block size.

vmkfstools is used for virtual disk management operations such as cloning and conversion, not for upgrading the VMFS datastore version, making this an incorrect remediation path.