Allocated File Size

Hello All,

Does anyone know why the allocated directory size (Size on Disk) on a MyPassport Wireless Pro (MPW) or a MyPassport USB drive connected to a wireless router port is so big? One directory (466,789 files/4,624 folders/102.9GB) on my new MPW is allocated 460.0GB. If this is holds for all directories, a 4TB drive would only hold 1TB? The allocated size is not as great for smaller directories, but still enough to significantly degrade available storage space. One 37GB directory is taking about 60GB on disk.

The allocated space for the same folders on a MyPassport drive connected directly to a USB port on my laptop or a WDMYCLOUD NAS connected to a wireless router Ethernet port is only 103.8GB.

I assume the extra space is overhead for file management that would otherwise be performed by the laptop or NAS? Is the extra allocated space only used as ram when accessing these folders? If not in use, is this space available for storing other data?

I am just guessing, but don’t see how the drive could be advertised as 4TB if allocated space is permanently not available. It would explain why a drive nearing capacity might not be able to access files during heave use?

I am just trying to get a better understanding of how allocated space affects available storage. I am not getting close to 4TB yet. Haven’t been able to find a good explanation.

Thanks for any comments,


I have been researching allocated size and see I was incorrect. The size difference is a function of cluster size of the disk clusters were formatted. I don’t totally understand, but one example shows allocated size double actual size.

That still doesn’t explain how the allocated size of one folder on my drive is 4X the actual size and why this only occurs if I am accessing the MPW wirelessly? If I connect the drive to my laptop via a USB cable, the actual/allocated size is 102.9GB/108.8GB/ If I access the drive via the MPW wireless network, the sizes are 102.9GB/460.0GB.