Bitlocker very slow. Taking days as appose to hours

So have a new 4TB drive and i thought it would be prudent to encrypt it using bitlocker, as i have done in the past with all my external drives.

I started bitlocker within the O/S and well after two hrs it had completed something like 0.2% so did a little searching around, and someone had mentioned its quicker to do this in recovery mode using the command manage-bde -resume driveletter: Don't forget to pause the encryption before restarting into recovery mode, and also see my tip below about making a note of the recovery key As you're going to need it.

Tip: Once in recovery mode, an easy way to find what drive letter is the actual ext drive you're trying to encrypt is type manage-bde -status and it'll list all your drives, and it'll tell you which one has the bitlocker encryption that should of already been started in the O/S.

Left it overnight, for 8hrs to be precise, and its done like 7% (again you can check the percentage of completion by using the command manage-bde -status

So at this rate, its going to take ages to complete this. I've never done a 4TB before, but i have done a 2TB before, and well it most definitely didn't take this long. Perhaps overnight or maybe 24hrs. This was using Windows 7, as appose to Win10.

I chose to encrypt the entire drive and did not take the newer encryption offered by Win10.

Also for whatever reason, my screen goes into stand-by while being left in recovery mode for sometime, and no-matter what i can't bring it out of it... so what i end up doing is typing blindly, manage-bde -pause driveletter: i see the drive light stops blinking, so i know its paused the encryption, then restart the computer. HOWEVER, because the ext drive is bitlocker protected, you'll have to unlock it, when you go back into recovery mode, using the recovery key that was generated when you first launched the bitlocker encryption within the O/S.... so top tip, take a photo or write that recovery key down as you'll need it.

At this rate, it seems like i'd be better off building a Win7 machine just to run bitlocker...

What's the deal with bitlocker taking infinitely longer to encrypt in Win10 as appose to Win7 ?

Who in their right mind over at MS thought ok we'll offer this, but it'll take a week or two to actually make any use of it, for what is nowadays a standard size of any external / internal drive.

So in future, should we be using 'free space only' on new drives ? if an external drive has never been used before ? I'm a little unclear on that and on how it works. Does it slow the drive or take extra time to copy data to it down as you add data to it, had i taken that option? Or would the adding data speed been the same, and using the 'used data only' option is ONLY risky if you've previously had confidential data on the drive prior?

There's very little discussion online or on the web regarding bitlocker & going by this thread, not a lot of people have answers.

Did i take the wrong option? Its been so far 40hrs, and my pc has been in recovery mode doing its thing. I personally don't know how much longer its going to take, as i'll leave it til i get back from work later this evening, then i'll check. (as it involves a restart and putting in that long recovery key to find out) But assuming its only going to be at 50% or so. Which is a bit of a joke ! considering this is supposed to be the 'fast method' If i was someone who only had one computer, it would be pretty restricting.

ok so checked the status of my drive that's been going non-stop for 48hrs, and its only done 28%

i'm not even sure i'm willing to keep my PC on in recovery mode for a full 24/7, just to encrypt this stupid drive !!!! I'm at the what do i do now crossroad tho !

Anyone know if i can use a windows 7 ultimate build to finish this off ?