High/Variable "System" disk usage

I have a 256 GB SSD in my Macbook Pro. Last I checked, a couple weeks ago, it had around 50 free GBs. Then today for no apparent reason, it had only <2 free GBs. I checked About this Mac -> Storage and saw that System was using 199 GB. Then I looked around for a usage analysis tool and before I could get through installing it, the System usage had dropped to 185 GBs. Then a few minutes later it was down to 150 GBs.

Now it is at 107 out of 256 GBs.

Is this even a meaningful number?

What is the System usage and percent usage of your storage?

Can you explain what might have caused it to jump up to 199 GBs, then come down to 107? Is 107/256 normal?

G'day and welcome to the forums.

By chance do you use Time Machine for backups to an external drive? If so it sounds like time to hook up the external.

I will do that. Just fmi, how many GBs and what percentage does System take up on your machine?

That is a meaningless number and your question is also meaningless. The display of disk usage on that particular utility is notoriously bad. The reason it was suggested to hook up the TM drive is that if you start TM, then disconnect the drive, TM creates "snapshots" on the internal drive until the external drive is re-attached and then it writes out all those snapshots to catch up. Since your System storage was going down so fast, the assumption was that somehow TM was using, then freeing, space for snapshots.

But then again, so can word processing, or browsing, or watching videos. The system grabs and releases disk space as it needs to to keep the applications functioning properly. So if your memory gets full and there is something demanding more, the system will write out to the HD some of the internal memory, then once the demand goes down, pull it back in from the HD. Get a lot of memory-intensive applications going at once and the system can take up a lot of room.

So, asking what Harry's space is on his machine is meaningless to you because his memory usage, memory available, number of apps running, etc, can and probably are, different from you and may be changing all the time.

What I think you might look at is Activity Monitor and look as the Memory tab. If it is showing anything under Swap Used: then your system has run out of memory and the system has used the HD for that overflow problem. If you can, get more memory.

Not sure why it posted twice, but to save screen space, erased the second copy and put this.