You need to exit from Lightroom and use your operating system tools to make room on you main HDD. You need to keep 25% of your drive capacity free for proper efficiency. i.e. if the HDD is 1 TB you nee to have 250 GB free. Check and see what is consuming the space and decide which files you can delete and which can be removed to an alternative drive.
25% seems pretty arbitrary and unreasonable.
With today's drive that means on a 2TB drive I need to keep 1/2 TB free. That means I am paying for 2TB with only 1.5 usable just to use LR. In my case where I have four 2TB drive I have to have 2TB free or equivalently have an entire drives worth of space (4*500M) I should not be using.
Even given that was true I get a similar message and it states I do not have at least 20M free on the drive where my catalog is. The drive where my catalog is has 800M+ of a 2TB drive free (exceeding the 25% rule).
And if you are talking about just the "C:" or "root" drive then I have a 250G drive with over 180M free. And neither my catalog or my pictures are on it.
Still looking for an answer.
It is very annoying to be in the middle of an edit and have the message pop up and stop the edit. Then you have to clear the message, undo the incomplete edit and start over hoping the message does not come back.
Any additional suggestions?
You don't have enough headroom on your c: drive, 180M is peanuts. Free up some space or get a bigger drive, they're cheap enough.
Sorry, I have 180G of space... not 180M. and it is an SSD so should be plenty of room and fast enough. Thanks for the response... Sorry I got it wrong...
That being the case I don't know why you are getting low disk space warnings. I have used SSDs half that capacity (60GB) and run Win 7 and Lightroom without any problems. Sorry I can't help.
There are a few threads on this subject, some dating back to 2014, with no definitive answer.
Yes, the 25% suggestion is certainly not reasonable.
Sounds like you have plenty of free space on you drives. Use your OS tools to do a check on your drive usage statistics.
The next time you get a "low space" warning, check your drive stats while the message is still up.
Inside of LR, go through your preferences and catalog preferences to see where LR is putting its caches and temp files.
The "low space" warning is a operating system warning not a Lightroom warning so I think you should be making inquiries on the forum of your operating system Mac or Win.
If you do not wish to heed the 25% warning that's your choice but while you will not experience a shutdown there will be some slowdown of the efficiency of the drive. Less than 10% you will risk damage to the drive and or loss of data.
To wit a 1 TB drive drive with 600 GB free space will be far more efficient than a 250 GB SSD drive with 80 GB of free space.
DdeGannes is simply relaying some pretty standard advice to keep your drives running at efficiency. If they get more than about 75% full in general they will start slowing down, so that is a simple rule of thumb that if you have a drive that you write to a lot, you need to have a reasonable amount of free space on it. However, your observations are incompatible with your drive having too little space. You said your 2TB drive that has images and catalog has 800 MB free. It should definitely not be giving you error messages. Also your startup drive has more than enough free memory (180 GB) for operating system swap files and more. Something else is clearly wrong. A simple thing to do is reboot if you haven't done that in a while.