Confused by free space Netgear104 in Raid5

[cirks]

I have a Netgear104 which has 4*2TB drives in it and is set to be running in RAID5. According to all Raid calculators this suggests I should have ~
5.5 TB usable space and this is confirmed by RAIDar as below so shows I should have 3.5TB free space as I have 1.8TB of files.
However, Explorer etc only reports 18Mb free at present and copying more data to the share reports diskfull.
What do I need to do to get the free space and make it usable or have I just made a fundamental mistake?

[Captain_Morgan]

Are you sure that B: is the nas mount & not perhaps a local Western Digital 2TB drive?

[cirks]

Hi - realised I was being stupid (no surprise there!). Yes, the B:\ is local drive that is backed up to the NAS and it's that which is full rather than the NAS :doh:
Doesn't help when of course folder names are the same in the locations so threw me and I was looking at wrong place for lack of space!

Thanks