Is it normal my 4TB LS520D NAS should only show 3.57TB available space?

[ChimpsInTies]

As title suggests. I have an LS520D nas with 2x identical 4TB Western Digital drives inside setup in Raid 1.
I only see 3.57TB usable space

Model: WDC WD40EZRX-00SPEB0
Capacity: 4,000,787,030,016 bytes [4.00 TB]
Serial No.: WD-WCC4E0KA6DHJ
Firmware Version: 80.00A80

I have the latest v4.50 firmware on the NAS

I understand that the NAS system itself needs some space and I also understand that drives are not truely what they are usually advertised as due to decimal and binary counting. However, does all this really account for a loss of 343GB? That's a lot of lost space. I just want to make sure this is expected.

I read somewhere a while ago that a lot of linux systems generally used to reserve 10% of the drive which used to make sense when they were small drives and we were talking a few hundred MB but now we're talking terabytes it's totally overkill. The main SSD in my PC is only 250GB and I have Windows 10 and all my apps running from that. What couple possible need this 343GB?

[Texturtle]

It's down to the difference between binary and decimal, Seagate has a good explanation on their website:

https://www.seagate.com/support/kb/why-does-my-hard-drive-report-less-capacity-than-indicated-on-the-drives-label-172191en/

[ChimpsInTies]

Thanks for that. I'd seen the calculation done another way somewhere else and it didn't work out to be such a difference. Saying that I may have just typed the numbers in wrong on my calculator. That site shows exactly the numbers I've got so I'm happier now.