USB HDD mount / unmount to reduce load on pi powersupply

One genetic question about mounting a USB HDD with raspberrypi/dietpi. If I mount the USB hdd at /mnt/userdata/usb which contains photo files only (not any operating system files). In ideal time that usb Hdd always rotating or will go to sleep/standby mode or not. if any application not calling data from that drive.
The reason for this is, my usb hdd suck power from raspberry & I do not want raspberry remain a unnecessary electrical load. My goal is to install plex on system & photos saved on usb hdd mounted drive. In normal we may be watch photos ones a week may be 30 min so I want that all other time this drive remain quiet & not consume much electrical power from raspberry also reduce wearing of hdd (as disk not rotating inside hdd). & raspberry pi power supply remain happy. I do not want to remove physically/manually usb HDD everytime. i do not have trouble in plex database management time that drive activate for small period & sleep again.
May be some body help to make easy mounting or unmounting process for usb HDD. Is it possible from outside we can make digital switch to mount or unmount the HDD. I have Home assistant running on different machine on same network. I can easily make automation switch on home assistant desktop but I need help to make batch files/commands & how can homeassistant controlling the system & give remote commands to linux machine . This way also look like more secure as if my home internet compromise the photos are unattached most of the time. So it give me feeling of more security. thanks


many thanks for your message. Depending on your drive, there should be an automated drive spin down (for HDD) via hdparm on /dev/sda

Thanks Joulinar, if system resolve this thing by default then i will happy to remain with default setting. thanks

we have some reports where the spin down was not working well. Sometimes it was needed to update HDD FW or use manufacturer software to activate spin down.