Lightroom cache problem "Mac HD is full"

[nu4_ya]

 See screenshot. Not sure why the cache is only 5 GB. Trying to move cache to external hardrive.
I Click on Mactinosh HD (cache on: Macintosh HD) and it opens a folder Lightroom Library.lrlibrary with other folders in it; the top folder with a long series of letters and numbers is hightlighted. 
I click on my Lacie External on the side menu. I thought at some point there would be a "Move Cache" or "create new cache" prompt but no. 
So I manualy coppied the folder Lightroom Library.lrlibrary, with all the folders in it,  over to my LaCie external. Thinking I could then just click on the folder with the long series of letters and numbers. But there is no "select" or "open" option, so it just stays on "Macintosh HD"
What do I do? I'm sure it must be easy. 1) either increase my cache size from 5GB or 2) move cache to external (much more free space). Step by step guide would be great. 
(by the way, for After Effect I was able to change or set up the cache for the Lacie External.)

[Anshul_Saini]

Hi @nu4_ya,

Thanks for the screenshot, that helps. A couple of key points about Lightroom (desktop) storage:

• The cache location cannot be moved to an external drive. Only the storage location for originals can be set to an external drive (which your screenshot shows is already pointing to LaCie).

• Your system drive currently shows 0 bytes free, so Lightroom can’t grow its cache beyond ~5 GB, and macOS itself will struggle. You’ll need to free space on Macintosh HD first; increasing the cache size won’t work until there’s free space.

• Reset preferences (hold Shift + Option while launching the app) if that doesn’t work.

Free up system disk space on Macintosh HD (target at least 20–30 GB free). Empty Trash, move non-photo files off the internal drive, remove large downloads, and quit other Adobe apps that maintain their own caches. Ensure the LaCie volume is formatted ExFat, APFS, or Mac OS Extended (Journaled) and that Lightroom has Full Disk Access in System Settings › Privacy & Security.

If you still see “Mac HD is full” after doing all this, please share:

• Copy & paste Lightroom desktop system info (Help > System Info)

• A fresh screenshot of Preferences › cache after you free space

We’ll take it from there.

Best,

Anshul Saini