If you are a very cautious person then you could turn off the computer before powering off the drive.
The middle ground is doing what you do - eject or unmount the drive and then unplug and power off.
The third option, if you are not a worrier is just to unplug it. As long as it isn't writing to the drive at the time it should be fine. But I guess, since you asked the question, that you're not that type of person, so options A or B are good.
ps it doesn't matter how careful you are, you have to count on the drive failing at some point, so make sure you keep backups of your important stuff
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For the sake of your own health and sanity, if your data is important to you, keep a second copy on another storage (a backup)
