Something like this seems like this would do the trick. I could leave my laptop in always on mode and still not draw much power. However I'm not sure how much power the HDDs themselves draw when idle...?
Whoops, forgot link.
https://www.amazon.com/Sabrent-External-Duplicator-Function-EC-HDD2/dp/B00IKC14OG
I would recommend something like this then. Rather than have your HDD sit at a weird angle (which can more quickly wear out the drive) or not be able to fit it at all, get a 3.0 (or w/e) external hard drive dock like this one: https://www.amazon.com/dp/B00IKC14OG/ref=cm_sw_r_cp_apa_pUDjAbEZ6XM9B
I've used this exact one no problem.
You can get something like this and use it's clone/duplicate functionality, but I'd only get something like it if you will have need for it again, otherwise just get another sata cable.
Buy a clone dock, we use them at work, it's a block level clone and doesn't require software, just plug the source drive into bay 1 and destination drive into bay 2, hold down the clone button for about 10 seconds until the lights start flashing and come back in an hour or so depending on the size and speed of your drives.
This is the model we use at work : https://www.amazon.com/Sabrent-External-Duplicator-Function-EC-HDD2/dp/B00IKC14OG/ref=sr_1_1?ie=UTF8&qid=1481577742&sr=8-1&keywords=clone+dock
I've cloned about 100 drvies with it over the last year, and had no issues with any of the clones.
I would recommend a clone dock, then use Windows Disk Management to extend the drive.
A device like this works great : https://www.amazon.com/Sabrent-External-Duplicator-Function-EC-HDD2/dp/B00IKC14OG/ref=sr_1_1?ie=UTF8&qid=1482269475&sr=8-1&keywords=sabrent+clone+dock
These are a life saver. https://www.amazon.com/dp/B00IKC14OG/ref=cm_sw_r_cp_apa_gsXiybBDMTQ3D Pop your mech in bay #1, ssd in bay #2 and let it do it's magic. After that, once a week, power off your system, put the ssd in bay #1, old hdd in bay #2 and back up your ssd. If the worse ever happens and you loose your boot drive, you can be back in business until you can replace the ssd, or if the Windows install gets corrupted and the ssd is still good, clone that back to your ssd.
Now, to answer your question, no your pc will allow you to change your hdd configuration however you see fit.
Something like this. Is it easier to skip removing the hard drive and just plug in an external? Absolutely.
My father and I (briefly) ran a computer repair shop and used something like this to recover data.
If the hard drive is actually toast it's a much taller order, though.
Order an HDD dock, put both in, you can get a program to transfer the files. You can check /r/buildapc for more info on this.
I got myself one of these a while back and it makes the entire process even more painless
Have you considered just getting a hard drive dock for whenever you need to plug in one of your dozens of hard drives?
It seems a lot more cross functional to me:
I have one of these that has served me very well since Feb 2015.
Sabrent USB 3.0 to SATA Dual Bay External Hard Drive Docking Station https://www.amazon.com/dp/B00IKC14OG/ref=cm_sw_r_cp_apa_JYeMBb7QZ8RAM
Buy a dual hard drive dock that clones like this. Then get a couple 1 or 2 TB drives.
My workflow is to import with lightroom into my computer. Then when I'm done with the raws, I drag the folder within lightroom to the external harddrive. The external clones itself every once in a while.
Uh, something like this?
Your drive is on its way out the door, simply put. I highly recommend getting a new one as soon as possible. In regard to cloning, hmm...my preferred method in your particular circumstances would be to do a hardware-based drive clone using something like this if possible, but I would advise doing that with a drive of equal size. If not, I am not too familiar with OS X drive cloning utilities, but it looks like Clonezilla supports OS X so that is one tool you could use.