How do I disable Spotlight indexing to prevent system files from filling disk space on my Mac?

You can try from the app store—

Storeograph —for some insights and resolve —67.3 MB in size only, if you can free up enough space to utilize this light weight utility

https://apps.apple.com/us/app/storeograph/id6754857256?mt=12

report back your success or failure.

or a Spotlight bug―

you can try from Activity Monitor clicking open and quit both processes <Spotlight> and “<spotlightknowledged>

if <corespotlightd> the root of troubles, delete all files under ~/Library/Metadata/CoreSpotlight/

This would be from the Finde>Go>Go to Folder copy and paste:

~/Library/Metadata/CoreSpotlight/

Command A will select all....

ref: Tahoe: Spotlight Doesn't Index and Search… - Apple Community

e2ipiminus1 wrote:

OK I restarted my mac & was able to get the files (deleted. All snapshots from today and yesterday. This has freed up 50 GB. I've been here before. This is treating the symptoms and not the disease. If time machine does the same thing in the next two days, I'll be back in the same position with no disk space.

Something is misconfigured.

This is the nature of my complaint. If I can't keep indexes and snapshots from filling disk. Im back doing disk surgery with diskaid every couple of days.

This cannot be the way the system is expected to be run

Time Machine will do the same thing, that is its function with the default backup frequency – hourly snapshots and it will save the last 24 hours worth of those locally (on your internal drive). They take space, of course, but that space is finite not continually expanding. My collected TM snapshots use 57 GB, and currently I have 841 GB on my internal drive. If I had a 1 TB drive, now is the time I'd be looking to reduce what is on it (I have >300 GB of photos and >150 GB of movies, which is where I'd start). I have 2 TB of storage, so I have plenty of space. I got 2 TB with this Mac because my last Mac (a 2019 16" MBP) had a 1 TB drive and it was at ~750 GB, so I knew I needed more next time.

Looking at your screenshot, you have 239 GB of photos – that is 'low-hanging fruit' in terms of something that's easy to store on an external drive (which you should also back up). You also have 140 GB of iOS files, those could be device software updates and/or backups. Those categories are places to start. Another place is the 95 GB in Other Users & Shared.

Following steps in user tip I posted in my first reply, or using the app that leroydouglas linked, you can investigate what is being categorized as System Data (other than the ~50 GB of TM snapshots). It's not Spotlight indices. If you won't copy off your own data from the obvious places, you need to figure out what is in System Data. Or you can keep going down this rabbit hole that you fell into when you let your drive fill up.

At the end of the tip I linked in the first response, I described the 'nuclear option' of erasing your Mac and restoring from the TM backup drive. That remains an option. But regardless, what you need to do is free up space on your Mac.

What makes you believe it is Spotlight indices that are taking up your storage space? How are you determining that?

Regardless, to answer your question about turning off spotlight indexing, follow steps 1-4 in this list:

Rebuild the Spotlight index on your Mac - Apple Support

If your assessment is based on System Settings > General > Storage, the System Data category, those are mainly your own data. See this User Tip:

How to free up ‘System Data’ and other st… - Apple Community

e2ipiminus1 wrote:

The problem is with the behavior of corespotlightd when the disk is nearly full. You are clearly NOT testing that. Fill your disk so that here is only about 5 gig left. I'm betting you will see dramatically different behavior. corespotlightd hits 90%+ of a CPU. At this time the system becomes quite laggy.

The problem there is not Spotlight, it's your disk being nearly full. You should always keep at least 10% space free (really free, see the post from @Owl-53 below), 15-20% is better. Absolute minimum is to have 20 GB free, and even then only temporarily until you can free up space.

If you have 5 GB free on your internal storage, your Mac is going to be in a bad state. Period. I have NO intention of testing that myself, it's like saying if you drive your car into a wall you at 30 kph then you will damage the car...it's not something that one needs to test, it's a simple fact.

You need to determine what is taking/filling up the space on your drive. It's not the Spotlight index. If it was, you'd see the Disk activity from Spotlight writing huge amounts of data, and if you excluded your drive from indexing as posted previously, the issue would go away.

The System Data was called the Other Category. The link will describe what files are in that category.

If you're using Time Machine a lot the following might help you in gaining back some real estate:

The corespotlightd process is always running. It's still not clear to me why you believe there is a connection between that process and System Data increasing.

In Activity Monitor, what shows for that process in the Disk tab? Nothing concerning in mine (but my System Data is a very reasonable ~30 GB of my 2 TB internal storage).

From another contributor @etresoft regarding Free Space and Available Space 

Free vs available disk space huge differe… - Apple Community

Quote >>  “ The "available" storage is the amount of used storage that the operating system could automatically delete if it felt that it was really necessary.

The "free" storage is the amount that you can actually use for something.

There are system processes that run in the background and automatically delete some of the "available" storage and convert it to "free". If you completely run out of storage, then those system processes will try a little harder.

When you "delete" files you are just hinting to the operating system that you don't need those files anymore. The operating system will eventually remove them, but on its own schedule.

Certain tools will allow you to force the issue and manually clean up some of this storage and manually delete local snapshots. But that is only temporary. "  << End Quote 

Purgeable Space is controlled by the Operating System and not the user 

Get detailed information about a disk in Disk Utility on Mac - Apple Support (CA)

Yes it may, as it Spotlight attempts to index all the changes as the Operating Struggles to find Free Space

And I concur with my colleagues' assessment regarding Free Space versus Used Space

Most responsive users never allow or attempt to purposely fill the drive to the point that Free Space drops below certain values

Some of which have already been mentioned earlier

To make the analogy to the Fuel Tank

Once it is full, hard as one may try. You just can not fill it any further

Below is a Real Life example of a Drive that Too Full to perform a simple upGrade

macOS installation fails due to apparent … - Apple Community