time machine backup an external hard drive

i have go around setting time machine.

have hard drive (pc, internal type) in external caddy. deleted old stuff & made backup overnight. has worked fine, have 2 questions...

have second internal drive in same caddy & usb drive plugged in mac well. backup "backed up" mac 1tb internal drive. can backup other 2 drives well?

secondly....as internal drive/caddy, safe remove (i.e. switch off) quite noisy & fear if running 24/7 fail. if turning off, assume drag logo recycle bin, in same way did (when logo "1tb external")

help, appreciated.

 

incidentally, add, have tried add other 2 drives. via system preferances, time machine. in "options" "exclude these items" 2 drives greyed out. cannot see or way in including them.

 

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