Why does external 1tb hard drive turn on and off during sending of files from c

[Denmac]

Hello,
why does a external hard drive switch on and off during transfer of files from PC C drive to external HD 1 TB. TB Drive goes away and then comes back into list 'explorer' window. Power to external drive is never switched of manually.

 

[blacksci]

probably because its updating the library after its loaded a file and your seeing that.