Two ~250Gb volumes "inhabiting" the same storage space?

[Kotze203]

Ok so I got an M1 MacBook Air from my school and when I reinstalled macOS (11.3) it let me choose between /Macintosh HD and /Data, which were both the same size. Because I couldn't figure out how to resize Macintosh HD after deleting /Data I decided to just use /Data for, well, my /Data and /Macintosh HD for everything else, much like I did with my Windows machines.

The thing is, I am pretty sure that my school must have bought the cheapest M1s, which come with a 256Gb SSD, so it wouldn't really make sense for me to randomly have a 512Gb one, and it also has 8Gb RAM (is there even a config with 8Gb of Ram but a 512GB SSD? And also, when looking at the storage, it coincidentally is always occupied in the same capacity, even though I haven't really saved anything to /Macintosh HD at all, because I was using /Data.

So, I guess my question is: Have I completely misunderstood what a "volume" is? Are the two volumes taking up the same storage space?
What is the "correct" or "factory" setup for a 256Gb MacBook Air M1 (I am not the first person to use this Mac)?

I've attached a screenshot of the "About this Mac" section to show you what it is looking like for me and also what it looks like in my Disc Utility.

Thanks!

 

[gilby101]

Yes, those 2 volumes are sharing the 256GB space. With APFS, the install process, partitions the drive to hold one APFS container/partition and puts volumes inside the container. By default, all volumes in a container can grow/shrink as required until all the space is used.

In Disk Utility you should enable Show All Devices in the view Menu (or hit command-2). That will show you the disk devices and all the partitions/containers and volumes inside them.

BUT, in your case you did the install wrong - though what you have done continues to work. You should have erased the disk (Apple SSD ...) and done the install into that. Then you would have (with default names) a single APFS container with two volumes Macintosh HD and Macintosh HD - Data. The first volume is the read only macOS system and the second has all the additional installed apps and settings as well as your files.

If you post a screenshot of Disk Utility with Show All Devices, we can probably help you tidy it up without starting again.

You will also see other small volumes (VM, Preboot, etc) also sharing the container.

PS. The About this Mac - Storage tab is at best incomplete and often just confusing. Disk Utility is much better.

 

[Kotze203]

Yes, those 2 volumes are sharing the 256GB space. With APFS, the install process, partitions the drive to hold one APFS container/partition and puts volumes inside the container. By default, all volumes in a container can grow/shrink as required until all the space is used.

In Disk Utility you should enable Show All Devices in the view Menu (or hit command-2). That will show you the disk devices and all the partitions/containers and volumes inside them.

BUT, in your case you did the install wrong - though what you have done continues to work. You should have erased the disk (Apple SSD ...) and done the install into that. Then you would have (with default names) a single APFS container with two volumes Macintosh HD and Macintosh HD - Data. The first volume is the read only macOS system and the second has all the additional installed apps and settings as well as your files.

If you post a screenshot of Disk Utility with Show All Devices, we can probably help you tidy it up without starting again.

You will also see other small volumes (VM, Preboot, etc) also sharing the container.

PS. The About this Mac - Storage tab is at best incomplete and often just confusing. Disk Utility is much better.

Thank you so much! I think in that case it makes sense for me to use /Data for everything except Applications, because I don't want to use the folders Apple has in the user folder. Here is the full Disk Utility screen:

 

[Honza1]

Thank you so much! I think in that case it makes sense for me to use /Data for everything except Applications, because I don't want to use the folders Apple has in the user folder. Here is the full Disk Utility screen:

I do not think you got the message.
You have NO CHOICE here. Apple decided, that your system will have following "disks"
1. MacintoshHD - this one contains ONLY system and is read only under normal use.
2. MacintoshHD-Data. This one contains everything else, including some user specific "system" configurations. SOme users reported having multiple Macintosh-Data volumes, one per each user. My systems have single such volume, but also only one real user.

During normal operation these disks are linked transparently together so in Finder and other browsing tools they look like one drive. You will never see these volumes in Finder or any other data browser as they are hidden.

Going outside this layout is going to be major challenge and well outside what Apple expects you to do. If you can make that work, you should make detailed post here and explain what you did, how you did it and how come it works. I think many readers will be interested.

On a side note: you can put Applications folder(s) anywhere, they are simple normal folders, nothing special. I have multiple Applications folders - common in normal place, my own private in my home directory and even some I use rarely on external SSD which is mounted only sometimes. So no need to partition anything to put Applications somewhere...

 

[Kotze203]

I do not think you got the message.
You have NO CHOICE here. Apple decided, that your system will have following "disks"
1. MacintoshHD - this one contains ONLY system and is read only under normal use.
2. MacintoshHD-Data. This one contains everything else, including some user specific "system" configurations. SOme users reported having multiple Macintosh-Data volumes, one per each user. My systems have single such volume, but also only one real user.

During normal operation these disks are linked transparently together so in Finder and other browsing tools they look like one drive. You will never see these volumes in Finder or any other data browser as they are hidden.

Going outside this layout is going to be major challenge and well outside what Apple expects you to do. If you can make that work, you should make detailed post here and explain what you did, how you did it and how come it works. I think many readers will be interested.

On a side note: you can put Applications folder(s) anywhere, they are simple normal folders, nothing special. I have multiple Applications folders - common in normal place, my own private in my home directory and even some I use rarely on external SSD which is mounted only sometimes. So no need to partition anything to put Applications somewhere...

I originally had another volume called just "Data" with the same size as Macintosh HD that I now readded by hitting "+" in Disk Utility. I am treating that one as my "user folder" from now on because I don't like how there is "Music" and "Movies" and stuff in the user folder Apple gives us.

So in my understanding doing that would be like partitioning in Windows where you have C: for the system and applications and all the crap Windows or some applications just randomly **** everywhere and D: for your Data, your own walled garden so to say. With the difference being that it is not actually partitioned and the actual storage size is dynamically allocated to the (for the lack of a better word) "virtual" volumes.

 

[Honza1]

I originally had another volume called just "Data" with the same size as Macintosh HD that I now readded by hitting "+" in Disk Utility. I am treating that one as my "user folder" from now on because I don't like how there is "Music" and "Movies" and stuff in the user folder Apple gives us.

So in my understanding doing that would be like partitioning in Windows where you have C: for the system and applications and all the crap Windows or some applications just randomly **** everywhere and D: for your Data, your own walled garden so to say. With the difference being that it is not actually partitioned and the actual storage size is dynamically allocated to the (for the lack of a better word) "virtual" volumes.

That should work, adding your own additional volumes will work as expected. Just you have to keep the MacintoshHD and MacintoshHD-Data for the system to work... Additional volumes is fine.
Advantage of the APFS volumes is, that they share space, so you do not have to decide on the size early. I always realized later, that sizes were different. And repartitioning was always bit challenge.
Disadvantage is, that you can run out of space globally - in another chain here (now) is one unlucky user, who run out of all space on his drive (has less than 4GB free) and now the system does not even start. This would not happen if there was way to keep some fraction of space preallocated for the system.

 

[gilby101]

I originally had another volume called just "Data" with the same size as Macintosh HD that I now readded by hitting "+" in Disk Utility. I am treating that one as my "user folder" from now on because I don't like how there is "Music" and "Movies" and stuff in the user folder Apple gives us.

So in my understanding doing that would be like partitioning in Windows where you have C: for the system and applications and all the crap Windows or some applications just randomly **** everywhere and D: for your Data, your own walled garden so to say. With the difference being that it is not actually partitioned and the actual storage size is dynamically allocated to the (for the lack of a better word) "virtual" volumes.

You are making things over complicated for little benefit.

You just need the configuration with the two volumes Macintosh HD (read-only macOS) and Macintosh HD - Data (everything else). These are created automatically when you erase this disk before installation. They are then combined (using 'firmlinks') by macOS to show as a single file system called Macintosh HD.

I have carefully used the term 'file system' which is a higher level construct than volume. The 'file system' shown as Macintosh HD in Finder and elsewhere is made of two APFS 'volumes' Macintosh HD and Macintosh HD - Data. The use of Macintosh HD for two different contracts (volume and file system) is very confusing.

Just keep to this default volume and file system layout. Everything except the 13GB macOS is stored in the volume Macintosh HD - Data, but is shown to Finder and other applications as the single file system Macintosh HD.

By default applications appear in /Applications which is a top level folder in the file system. The actual storage used in partly on the read-only volume (core macOS apps like Mail) and partly on the read-write volume - but this is hidden from the combined file system.

Your data files (settings, documents, photos, whatever) are, by default, stored in the folder tree below /Users/<user>/. This keeps them sufficiently separate from macOS, applications and system wide settings.

So DON'T create a separate volume for your data. Just use /Users/<user>/...

And DON'T try to recreate what worked for you in Windows. This is a different operating system with different advantages and disadvantages.

 

[Kotze203]

Your data files (settings, documents, photos, whatever) are, by default, stored in the folder tree below /Users/<user>/. This keeps them sufficiently separate from macOS, applications and system wide settings.

So DON'T create a separate volume for your data. Just use /Users/<user>/...

I understand that. But in that user folder are folders created by the operating system that I don't intend to use, can't delete normally and if I would then they would be recreated when updating or reinstalling the operating system. I don't need a movies folder, or a music folder, or anything like that and I don't want my actual Data living next to those folders because that is messy. I appreciate that macOS lets me create a new "virtual" volume as you have pointed out, just to keep things organised to my liking, not having to deal with the file system like Apple intends (except Downloads and Applications I guess).

But that is a whole other story!

Thanks for clearing up my confusion about the volumes. Now, my last question would be: Looking at the Disk Utility screenshot from my second post (which I will attach to this post again), is that the configuration that one would get "out of the box"? Because in your first post you mentioned that I did the install wrong?

 

[gilby101]

Thanks for clearing up my confusion about the volumes. Now, my last question would be: Looking at the Disk Utility screenshot from my second post (which I will attach to this post again), is that the configuration that one would get "out of the box"? Because in your first post you mentioned that I did the install wrong?

That looks right for out of the box.

Sorry, I think I was confused because you wrote about having a '/Data' volume.

I don't need a movies folder, or a music folder, or anything like that and I don't want my actual Data living next to those folders because that is messy.

I used to fight with how Apple likes to layout the 'user' folder. But it is much simpler to accept what is there. Having said that, there is nothing to stop you deleting Music, etc. The only folders you can't remove are (I think) Desktop, Documents, Downloads and Library. In the long run, I think you will find it helpful to have Music and Pictures folders and some apps will expect to find them - so for now leave alone and let them be empty.

It is fine to create more folders with your own names. So you can create a Data folder alongside Documents, etc. - its full path would then be /Users/<user>/Data which is usually abbreviated to ~/Data. Having created the folder you can drag it to the Finder sidebar favorites for easy access.

 

[colourfastt]

From this thread, I gather we're supposed to have a "BS" volume and a "BS Data" volume, but I have a "Catalina" volume and a "BS" volume (in addition to the data volume). The Cat. and BS volumes are apparently sharing the same space, but when most of my apps installed they went to the Cat. volume. It's all a bit annoying.

 

[gilby101]

From this thread, I gather we're supposed to have a "BS" volume and a "BS Data" volume, but I have a "Catalina" volume and a "BS" volume (in addition to the data volume). The Cat. and BS volumes are apparently sharing the same space, but when most of my apps installed they went to the Cat. volume. It's all a bit annoying.

It is supposed to be like the screenshot 3 posts up. From what you say, yours may be worse than just annoying. You risk increasing problems by having weird volumes. You may want to consider a backup - erase - reinstall - recover.

 

[colourfastt]

It is supposed to be like the screenshot 3 posts up. From what you say, yours may be worse than just annoying. You risk increasing problems by having weird volumes. You may want to consider a backup - erase - reinstall - recover.

After reading your post, I went and checked using DU and this is what is reported—it's rather odd that the "BS" volume is greyed out and that I have 2 "data" volumes (one "Data" and one "Data-Data". Thoughts would be helpful.

 

[gilby101]

After reading your post, I went and checked using DU and this is what is reported—it's rather odd that the "BS" volume is greyed out and that I have 2 "data" volumes (one "Data" and one "Data-Data". Thoughts would be helpful.

Everything I suggest here is at your risk. Make sure you have a good backup before making any changes.

As you are aware there should be just 2 volumes. Looking at yours:

1. 'Catalina' is the read-only System volume. Unusual, but I say this because it has an active snapshot com.apple.os.update....

2. The volume 'Big Sur' looks like a duplicate of that (its size is nearly the same as 'Catalina'). Most likely it can be safely deleted using Disk Utility.

3. One of the other two must be the active Data volume.

Can you provide the output of these two Terminal commands:

diskutil list
diskutil apfs list

As an aside, in Disk Utility it is often helpful to show the disk device, container, and volume hierarchy. Do this by either doing keyboard Command-2 or Menu - View - Show All Devices.

 

[colourfastt]

Everything I suggest here is at your risk. Make sure you have a good backup before making any changes.

As you are aware there should be just 2 volumes. Looking at yours:

1. 'Catalina' is the read-only System volume. Unusual, but I say this because it has an active snapshot com.apple.os.update....

2. The volume 'Big Sur' looks like a duplicate of that (its size is nearly the same as 'Catalina'). Most likely it can be safely deleted using Disk Utility.

3. One of the other two must be the active Data volume.

Can you provide the output of these two Terminal commands:

diskutil list
diskutil apfs list

As an aside, in Disk Utility it is often helpful to show the disk device, container, and volume hierarchy. Do this by either doing keyboard Command-2 or Menu - View - Show All Devices.

Thanks for your input. I've attached the outputs as screen grabs as well as the ⌘-2 list.

 

[gilby101]

As you saw, Disk Utility is much clearer when you are showing devices. And the diskutil output halls to add a little more detail but is essentially telling us the same thing. The volumes you have:

Preboot, Recovery and VM are all created by the install and look normal.

Based on snapshot mounted as / the volume named 'Catalina' is your read-only Big Sur system volume.

Based on mount points (and sizes):
'Big Sur - Data - Data' is your Big Sur data volume. It is 252GB and mounted at /system/Volumes/Data.
'Big Sur' and 'Big Sur - Data' are both small and, at a guess, are remnants from Big Sur installation attempts.

So (after ensuring you have a good backup), preserve anything important on 'Big Sur' and 'Big Sur - Data'. Then unmount and delete the 'Big Sur' and 'Big Sur - Data' volumes using Disk Utility. You would then have 'Catalina' and 'Big Sur - Data - Data' as the two parts of your Big Sur operating system. That should leave your disk a bit tidier though the naming of volumes is ugly. Do this at your now risk, but you would be covered against disaster because you have a good backup.

To get things looking better (and what I would do) is to start again:
Unmount 'Big Sur' and 'Big Sur - Data' using Finder or Disk Utility.
Backup using Time Machine,
Boot to Recovery,
Erase the whole disk (that is the disk device, not volumes),
Install Big Sur (internet download),
When suggested by the install, use Migration Assistant to recover all your data, applications and settings from the Time Machine backup
After complete, don't let Time Machine use your existing backup disk until you are sure everything is recovered - better to keep it on one side and use a new disk for Time Machine.