Will ejected internal HDD really stay ejected until I mount it again?

I want to get 2TB HDD in addition to 512GB SDD I have.

I want to be able to "turn off" that drive so that it stays off even after sleep cycles and everything... I'm worried because now when I have an external HDD and I eject it, it wakes up sometimes - for example just by launching Finder which accesses it... not sure, maybe it happens only after I wake computer form sleep, but still... I really don't want such behaviour in an internal HDD. It should stay "dead" until I resurrect it only when needed. Is this possible?

I don't know why is this information so hard to find - nobody reported it, just guesses and partial solutions on forums... So anyone with such setup - can you try?

I suggest to test and use: Disk Arbitrator.

This is a small application interfacing the MacOS X disk access interface. This application may be used in forensic investigation, to protect against unwanted connection of external disks, and to manage very straightforwardly any mounting and eject of internal or external disk (through the Show Disks Window menu entry).

I wouldn't speak in place of the author, but I can ascertain this tool is working on: Lion, Mountain Lion, Mavericks & Yosemite.

I haven't found any bug in this application, and I would be glad to give the same nul result with many application I have to survive with :(.

It won't stay ejected. When you reboot it'll be reattached. You can, however, fix this. I had to tackle the same problem when my internal drive failed on my iMac. The key is to tell the OS, via /etc/fstab that you no longer want it to mount the drive.

To do this you'll need the UUID of the drive. You can get this from Disk Utility. With the UUID in hand you'll make an /etc/fastab entry by opening a terminal and typing:

> sudo vim /etc/fstab

And then putting the following in there:

# Internal iMac HD that's dead
UUID=1B39A092-75B2-357E-97FB-23C082975B80 none hfs ro,noauto

Replacing the UUID in the above line with the UUID of your specific hard drive.

Here is the specific block of text I kept in my /etc/fstab file until I replaced the drive: https://gist.github.com/ianchesal/7389200

That chunk references this question and answer: Prevent BootCamp partition from automatically mounting -- which is where I got this solution originally. It worked great to keep that bad drive out of the way until I could crack open the iMac and swap it out.

Eject is only temporary, once restating the computer will read the disk again if it is still plugged in or you freshly plug it in.

So use the unmount in disk utility that is permanent till you mount it again.

I forgot, also disable the Spotlight search for that disk, so it wont spin any more.