I was just wondering if there is a way to make an HDD shut down entirely (that is, it stops spinning) while it is still connected to a running machine, as a power saving measure? This would be in a scenario where a different drive is used for OS/programs and the particular drive I would like to "sleep" is just a media/large files/seldom used applications dump. Would be pretty neat, decrease the size of the foot print and all. Thanks for any responses, see you in the comments!
western digital green hard drives do that. although I don't think software controls when HDD's spin up. they tend to spin up when the PSU gives them power, and I think the Heads start moving when data is requested over the SATA connection. If you want energy efficiency, WD Green is where it's at. although Green Drives don't support RAID, so don't even try. has to do with variable startup speeds.
I actually have a WD Green in my build right now. I guess I've had it all this time without knowing it. Kinda. Not really. It's kind of sad how much power an HDD uses as compared to an SSD, especially when idle. But oh well, they are getting cheaper so maybe I can replace my 120 GB (which is plenty for me) SSD with a larger one at some point. Probably gonna wait for SSD DIMMs (or whatever they are going to be called by then). Really looking forward to it.
By the way, my technical computer science professor said that at some point when RAM is replaced by some kind of NVRAM that operates at RAM speeds there will be strange things (in today's understanding) happening like OS crashes persisting through reboot cycles. Which I thought should be easy to solve since the OS could just set a "shut down cleanly" flag somewhere in its file system as the last thing upon shut down so the boot loader knows what to load upon boot, the "old" boot of the OS that has been suspended to NVRAM when the "shut down cleanly" bit has been set or the normal startup when it has not been set. That should fix the problem.
Anyway /tangent. Thank you for your response.
Edit: I just looked up the WD Green specifications and they use 3.3 when reading/writing, 2.5 when idle and 0.4 when the PC is in sleep mode (in Watts, these numbers are for my particular 1 TB, 3.5" model). What's neat is that the 2.5" Greens actually take way less power, about half as much when reading/writing. Source Which of course should come to no surprise because I would assume for smaller platters to experience less friction due to the smaller surface area and weight, hence the lower power required to accelerate the platter back up to the right speed. Are there any downsides to using 2.5" drives when compared to 3.5" drives of the same capacity? This is about 1-2 TB of total storage per drive. I will google it (and edit my findings into this post) because who even reads to the end of this wall of text.
Edit 2: 2.5" drives have smaller capacity, smaller cache and on average slower RPMs than 3.5" drives. So they usually offer less performance when compared to a 3.5" drive of the same price. Source
Greens are designed to slow or stop spinning when idle at the cost of slightly slower access times due to spinning up.
On GNU/Linux you can use hdparm to set when a drive should spin down, this should work on any drive, greens may or may not accept this command becuase they have code to manage it, you might have to test it.