You can normally drag and drop batches of selected images between folders. I don’t know whether there is a size limit for folders but it’s safer to use the OS.
When dragging and dropping you are asking LR to copy a new file, delete an existing file and update the catalog links all in one task. With large folders there is the potential for things to go wrong or for a system crash.
If you drag the folder in the OS you are undertaking a separate copy command. Updating Folder Location gives you the opportunity to check that everything is working before deleting the original folder of images from the disk.
Inside LR this is not possible, one has to do this with the OS and then telling LR to update Folder Location... Isn't this absurd ?
No, it isn't absurd, it makes perfect sense to me. And no, you shouldn't use Bridge for this, if you are using Lightroom, then you should use Lightroom or your OS for this. And yes, it is possible to do in Lightroom, as 99jon has explained, but the better way is using your OS and then updating folder location.
I am going to guess that the reason you are having troubles is that LR does not know about your new hard drive as you have never imported anything from it. Otherwise, you should be able to move the files.
However, in all honesty, you are much better off using the OS tools to move/copy the files then "relocating" the top-most folder(s) inside of LR. This will be much faster and less error prone.
Well, I know all this and I knew how to do this (doing it for years), but my question is why can't LR do this ?
Why can't a 'simple' thing like moving a folder from disk to disk be so hard to do ?
If browsers can, why not LR ?
I'm tired of doing simple things the hard way !
Lightroom is not a file browser. It was not intended to do the exact same things in the exact same way as file browsers.
And I think moving a photo from one disk to another in Lightroom is ridiculously simple.
LR could be...
As I said it's not a photo but a Big Folder. A Folder with 30+ subfolders with in total 16469 hires files !
Moving a directory tree of 30+ subdirectories and over 16K files to a new drive is not a simple task, regardless of how simple a file browser makes it seem.
Your best bet is still to move the directory tree using your file browser, the reconnect the root directories in LR. You will be much happier with the end results.