HDD mining is new thing which I have heard, as I know you can simply mine with sata drives, it doesn't cares about ssd, you need huge amount of storage, for example 100TB to get profit from hdd mining. Nowdays more known coin is burst and you can mine it, also it's profitable now. If you are now investing money, than as one member told you, it's better to invest GPU mining.
It depends on your situation and your goals (mining BURST)...HDD you make already have, how long you're going to hold the coin. In my case I already had about 12 TB (will probably increase that), my computers are always on, and electricity costs rolled into the business.
But you certainly don't need 100 TB to get the ball rolling.
With your 12 TB you are going to earn about 17$ per month. That is in my mind not very profitable. 4TB HDD is 129.78$. That means for 12 TB I have to pay 519.12 $. At current price it's going to take me 2.4 years to ROI. Now even if you already have hardware are you sure you want to spend all that space and your time managing your rig for 17$ per month ?
electricity cost for a single hdd is very small, the consumption is like 6w per hour, just do the math it's almost nothing monthly, i'm sure the problem is more about how many you need just for a few cent
