Turning off second HDD

jumanji idea will work to the best of my knowledge.

I personally use HotSwap bays. You will have a sata connection. Plug a ssd or hard drive in and then just use it as need be. When done just remove it and put it some place safe.

First, you are to be commended for having the good sense to have a backup! So many people do not, then show up here or on another forum distraught because their HDD with all the family photos, doctorate's dissertation, whatever, died and they didn't have a backup.

Storing backup drives outside the computer is the safest way to store them. I have a 2.5" hot swap bay built into my case and I added a 3.5" hot swap bay in a 5.25" bay. I just plug in an internal type 3.5" HDD into the hot swap bay to update my backup, then remove it and return it to the drawer I keep it in. Easy peasey, quick and slick.

An alternative to adding a hot swap bay to your computer would be to get an external dock, set it on top or alongside the computer, and leave it connected to the computer all the time. Just remove the backup HDD when not updating the backup.

There are switches available for shutting down HDDs (Orico and Lian Li are two manufacturers I've seen make them) that fit in a 5.25" bay. However, even if you use a switch or go inside the computer to disconnect the backup drive, you run the risk of losing the backup if good ol' Light Fingered Louie exercises his five finger discount and your computer and backup will both go south. Having the backup in a separate place from your computer dramatically reduces the chance of losing both.

Also, even if you keep your backups in another room, a fire, storm, meteor strike, etc. could still cause you to lose all your data, including the backup. Keeping a second backup offsite, such as in a locked drawer or locker at work, a trusted friend's or relative's house, or a bank safe deposit box will dramatically reduce the amount of data you would loose in a dramatic disaster, the amount depending on how often you update the offsite backup. Another way to have an offsite backup that is easier to keep up to date is to use a good, paid, backup service, such as Carbonite.com, Crashplan, or Backblaze. These have software on your computer that will encrypt your data before it ever leaves the computer. Just stay away from cloud storage sites, especially the free ones. They rarely are secure and the free ones are notorious for disappearing with little or no notice.