Mounting a hard drive as a folder in Windows?
Sophia Terry 
Why would you mount a hard drive as a folder? I am asking this because I have a 120gb SSD hard drive that runs Windows 10 and I also have a 1TB HDD in this computer as well that I have not partitioned yet.
92 Answers
If you are referring to Windows' option to mount a hard drive as an NTFS (the file system windows runs on) Folder. This folder will appear on your other hard drive, but not take up any space on it.
This means anything you put inside that folder actually goes onto the hard drive.
The benefits are that you do not need to map extra drive letter and it allows you to continue to use a logical folder structure if you have one.
Its not a fantastic idea in practice, as it hides where the files actually are which can be confusing. I'm not sure how windows reports the capacity usage on a drive in use like this, you may have to right click and look at the folder to see usage rather than being able to go to "my computer" and seeing quickly.
1I have been experimenting with mounting a large HDD to a folder on an NVMe drive to facilitate my Lightroom workflow. I sort of like it but I'll have to give it some time. I have my import folder, on the NVMe part and then move the RAW files to the "Long Term Storage" folder, once my initial edits are complete, which is an 8TB HDD. There is a lot more to it but that's the short version. I think this might help me maintain my workflow and catalogs even if adding additional HDDs at some point.
I've found that it is easy enough in Windows 10 to switch between mounting to a folder or a drive letter, without loosing any data. You can also do both and have the same files available through a drive letter or a folder structure. To do both Just choose "Add" without first removing what you currently have.
When mounted to a folder only, the folder will display the full size of the drive in the file size column of Windows Explorer. That large number is easy to spot and let's you know there is something different going on with that folder. I also changed the folder icon. To see the used and remaining disk space you must right-click the folder, choose 'Properties', and then click the 'Properties' button on the 'Properties' page. Hopefully that makes sense. Not as easy as just looking at 'This PC'.
I've found is that I cannot run a Samsung Magician benchmark unless mounted as a drive letter. I also do not see the drive separated out with utilities like CCleaner or Norton AV. Running a scan on my NVMe will also scan the HDD drive, for example.
You also cannot set a paging file on the mounted folder drive unless there is also a drive letter, if that matters to you.
Charlie was probably right that in practice it may just be too much trouble and confusing. I also have to consider if anyone else in the family could make sense of the configuration if I wasn't around to explain it.
