Actual File Size differs big time to allocated size

[kan]

I have a LinkStation 200 Series NAS with two 1Tb drives mirrorred. It is mapped  onto our peer to peer network for all Windows 10 PC's to access. When accessing through Windows Explorer, the allocated size is 1000% more than the actual file size -  ie.  1Mb file is allocated 100Mb .   Nas Navigator shows the drive 65% of the total 919MB available.
When trying to backup the NAS to an external usb 2Tb Drive, get an error out of space.  Any ideas?  Thx

[mc2]

The LS220 has a cluster size of 128MB, i.e. the space any file takes is a multiple of 128MB, which makes the LinkStation unsuitable for storing lots of "small" (much less than128MB!) files.

However, it also seems to sometimes greatly over-allocate larger files.  I put in a report about that a month ago, but have had no response ... http://forums.buffalotech.com/index.php?topic=24915

[oxygen8]

All Linkstations have a cluster size of 4kB, i.e. the space any file takes is a multiple of 4kB
Only the allocaded space message from samba is buggy.
All programms who use this message will show wrong values.
The drive summary will reported correct.