"Unknown" space problem

[FRAGaholic UK]

I recently bought a new build that is great, but now i have just noticed that i am missing about 1tb of storage on my second storage drive.
I have used windirstat and spacesniffer and found that there was 946gb of "unknown" space that is "yet to be scanned". I have tried to google it but to no avail. i don't know what might be causing this and i am hoping for any advice or help.

Here are my PC specs:
AMD FX-6300
Gigabyte GA-990-FXA-UD3
Corsair vengeance 8Gb (2x4Gb)
Asus GTX 550 Ti 1gb
Hitachi 750gb (OS drive)
Samsung HD204UI 2TB (Storage)

I am running Windows 7 Home edition 64-bit.

 

[phil22]

Have a look in Disk Management. It may simply be unallocated (unpartitioned) space.
Control Panel > Admin Tools > Computer Management > Disk Management
Look in the bottom-right panel and find the ribbon which relates to the storage drive.
It may reveal more info about the "unknown" space.

 

[FRAGaholic UK]

I have just had a look and it says that all of the drive is the same partition and that there is no "unknown" space, even though windirstat and spacesniffer says there is.