Is it possible to set up and external hard drive on my 2018 iMac such that it would automatically be treated as an extension of the internal drive(s)?
iMac 27″, macOS 10.15
Not that I am aware of, however what many experienced users do is to put their media (movie library, music library, photo library) on an EHD. This saves quite a bit of space on the internal drive and is very simple to do.
Some pro apps (Final cut Pro and the now no longer existing Aperture) would allow you to automatically "park" some space hogging project files onto an external drive, but that is about as close to making it an "extension" as you could get. As rkaufmann87 noted, you can put your libraries there, but that really isn't an extension either. You can also put your User folder on an external and direct files to a folder within your User folder. Most of this is "manual labor" though as you need to direct the files when you create them.
But, remember, that you will need a backup of that external drive if that is the only location for some of your files.
Yes, then testing them, and once you verified they are okay on EHD you can erase them from the internal HD. Apple explains an example for the photos library in https://support.apple.com/en-us/HT201517
Thanks, It's kind of what I thought but I thought I'd ask to see if someone knew something that had escaped me. I use Time machine and have a TB WD drive devoted to that. I just ordered a 2 TB drive since my internal drive is getting full. I suspect I have to ditch some apps that I'm really not sing as wel.
Assuming the OP is using Time Machine, Time Machine should backup the EHD. However, it isn't a bad idea either to have a scratch EHD to use as a secondary backup for the media EHD. When it comes to backup, redundancy is very wise.
By draggng the libraries to the new disk?
Yes, I also have a separate drive that I occasionally use to clone the main start-up internal drive.
External hard drive as an extension of the internal drive
