Raid 5 Question

[nantucket66]

I have a QNAP TS431 and at the moment I have 4 drives fitted -

WD Red 3TB x 3
WD Red 4TB x 1

All set up as single volumes, if I reformat them and set the QNAP up as RAID 5 will the parity disk be a 3TB drive or the 4TB drive?

Thanks

 

[nantucket66]

Sorry, bad wording on my part probably.

If I set up with raid 5 with 3 x 3TB and 1 x 4TB drive how much usable space will I have? I realise if it were 4 x 3TB it would 9TB, just not sure with 1 drive being an odd size. Thx