How are my hard drives configured on my DS5100?

[HankTheCat 0]

As mentioned in other threads, I am trying to setup a replacement DS5100 I received from Western Digital.  It came with two hard drives, and they appear to be the same size as the current drives.

 

What I did was put the old hard drives in the new DS5100 and booted up.  All my data was there and I was able to configure the new machine to my liking.  However now I have a question about how these drives are being used.  From the screenshot, you can see D: shows 1.53TB free of 3.63TB available.  I also included the view from Disk Manager, as well as from the WD disk utility.

 

What is going on here?  Is it combining drive 1 and drive 2 (each advertised as 2TB) to make a 4TB D drive?  In the event a drive goes bad, this means I’m unprotected, correct?  How can I get to a state where I’m protected in case of a drive failure?  Assuming I want to keep 4TB, would that require me getting two new 4TB drives and then adding them in a mirroring RAID configuration and then copying the data from D over to that new raid drive?

 

BTW, here are some screenshots of what I’m seeing.

 

 

Edited October 23, 2017 by HankTheCat

[Drashna Jaelre 159]

The D:\ drive is in a hardware RAID array, from the looks of it. 

 

This looks to be a RAID0, where one disk fails, and you lose everything.  

 

that's why these two disks are showing up as one, and 4TBs, but the other disk just shows up normally.