Trying to figure out Raid 1 for my set up?

[moresnowdays]

I posted a question in the storage section, but not sure if that was the place for it. I also not really sure how to ask what I'm looking for.

basically I have currently 4 hardrives.
-SSD- for OS and Software
-HDD- 1Tb WD Black for Working on Photo jobs, and my other documents
-HDD- 2Tb Seagate for storing my portfolio work
-HDD- 1Tb WD Green for archiving photos (gets replaced annually, and old ones stored away)

There is a 24hour sale today on Newegg for the same WD Black HDD I use as my working drive. I thinking I should buy one, and use it to put into RAID 1 with my current WD Black drive for constant back up. This is the only drive that is really critically for me to have constant back up.

Should I buy this drive, put it in the last HDD bay in my tower, and put into RAID 1 one with current working drive?

Or should I buy this drive, and an external enclosure, put it into RAID 1 one with the current drive? This way I can easily remove it and store it somewhere safe when I want to, or take it with me.

I don't want to lose the speed I currently have either if possible. Which should I do, and then I will have to figure out how to do it best?

 

[EarthDog]

One thread in the right section is best... will reply there.