Why Is My Mac System Storage So Big?

Mac users often freak out when they look at the Storage settings in About This Mac and find that System storage takes up way more space than they think it should. However, if they wait a bit the storage meter will continue to calculate what takes up space and allocate it to iCloud Drive and other things. Even once this is done, a fairly large System storage amount can be accounted for by looking at your System folder, system Library folder, and user Library folders.
Video Transcript / Captions
Closed captioning for this video is available on YouTube: Why Is My Mac System Storage So Big?.

This is a question I hear over and over again. Online, on the Apple discussion groups I get asked it. It's asked in other forums all over the place. Why does the system storage on my Mac take up so much space? If you go into About My Mac and then go to Storage, then go and look at the bar for System Storage, sometimes it can look alarmingly big. Well, I'm going to tell you why you probably see it as looking really big, why it's probably not as big as you think, and how to find out what really is taking up the space.

First, looking here notice what happens when you first go to Storage. You'll see that you get a kind of general like used and not used. Then after a while it starts to divide up in sections. When it first does this System Storage looks huge. So in my case it's almost 90 GB. A lot of people make the mistake of stopping here. They figure something's wrong and they go to investigate it or not investigate it or complain or whatever. But what they don't do is they don't wait because it's still calculating. It's still going to try and figure some things out. It takes awhile.

I'm showing you this in real time. So you can see now it's still not updating, it's still not updating. It's still just shows you that it's at 90 GB in System Storage and leaving you to guess what's wrong. I really think there should be a little message there stating still calculating or something like that. But if you wait long enough eventually it will begin to divide things out. What it's doing there is that it is looking in the system and library folders and it's figuring out what's inside there. If it finds something that belongs in another category it will move it to that other category. But it takes awhile. So if we wait long enough we will see it change.

There, it just did. You can see it took a big chunk and it put it into iCloud Drive. So iCloud is actually accounting for a lot of what was previously seen as being System. The thing is that in one of the Library folders is an actual folder that can change the data for iCloud Drive files and other things. So it sees that as being part of the System folder. It reports that back. As it gets more information about what's in the System folder it says, ah I can break this out and put it in another category.

Now even though 50 GB of System Storage is now allocated to iCloud Drive, 40 GB still seems too big, right. So you want to investigate. Now unfortunately if you go to Manage and you look you're just going to be told the same thing. There's a lot taken up by System Storage. But you have complete control to be able to look in the folders on your Mac and figure out what's what. So why not do that?

Now I happen to know that System Storage is going to be in both the System folder and the Library folder. So the first place I want to look is at the computer level and look at the System folder and use Command i to get info and then see how big that is. Then do the same thing with the Library folder. Using that I can account for half of System Storage. But only half. So where is the other half?

Well, there are two Library folders. There's a Library folder for the system and there's also a Library folder for each user. I go into my User Library folder and you can get to there by going to the Go menu. You won't see Library there initially but if you hold the Option key down on your keyboard the Library appears. You can go to the Library folder. Looking in the Library folder I can see that it's huge. Also I can see that there is a folder in there that is the iCloud Drive data I saw before. But also other folders that are taking up lots of space as well.

I can look in those and get an idea of what it's being used for. It's being used for cache files. It's being used to cache my iCloud Photo Library so I have some of the photo images there. It's being used to cache files, being used to cache things for Safari. It all seems accounted for and it's all being really well used because I have this space on my drive so my Mac knows that it should use it to try to speed up my experience. If I was shorter on space so I didn't have much space on my drive it wouldn't use so much. But since I have that space it's using it very wisely to give me a better computing experience on my Mac. That accounts for all of the System Storage space. There's mystery there. It's all accounted for and it all makes sense.

Comments: 3 Responses to “Why Is My Mac System Storage So Big?”

    Peter Buckley
    3 months ago

    Good topic but no mention of indexing which is also relevant. Apple recommend indexing to clarify

    3 months ago

    Peter: Not sure how indexing applies to this. Can you clarify?

    Peter Buckley
    3 months ago

    Large files could be caused by indexing issues. Snapshot first aid then re indexing the drive. My system file was 537 Gigs system crawling. Many coloured balls. Combination of your advice and apples sorted problem system now 33.4 Gigs cheers Garry

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