(Un)mount internal HDD at will I recently installed an SSD and made it my boot disk, and installed a 1TB HDD on a Caddy, where the DVD-ROM used to be. The one drawback is that having a second drive actually lowers the battery life quite a bit, so hence my question:

I know I can unmount the drive (eject it) so that it doesn't spin when needed, but, is there a way to re-mount it without having to reboot the Mac? I don't mind if it's a terminal command.

Thanks in advance :)
I'm assuming that you're talking about ejecting the drive using the the Finder. If so, then simply unmounting the disk, as opposed to ejecting it, should allow it to remain in the list of attached disks so that you can re-mount it later. For example, using

diskutil unmountDisk &lt;device or name&gt;

in the Terminal can be used to unmount the disk, but still leave it in the available drives list which can be seen by using

diskutil list

which can also be used to discover the &lt;device or name&gt; you require. Then to re-mount the disk you can use

diskutil mountDisk &lt;device or name&gt;

Note that all the above can also be done using the built-in Disk Utility application, just use the Mount/Unmount button as opposed to Eject.