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Any idea what "Volumes" is on my iMac HD?


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I recently noticed that the hard drive (3 TB fusion drive) on my late 2015 27" iMac (macOS 11.1) was more full that it should be (pre-dates the Big Sur update). When I ran Daisy Disk as Administrator, I found something odd. The top level of the HD has the usual 4 folders: Applications, Library, System, and Users. But it also had a folder (not visible in the Finder) called "Volumes," and in that is another folder called "iMac - Data," and in that are the same 4 folders that exist at the top level of the drive: Applications, Library, System, and Users. This mystery "Volumes" takes up ~1 TB vs. ~1.4 TB for the rest of the drive.

What is this "Volumes," an apparent partial duplicate of the rest of my hard drive? How do I get rid of it or at least shrink it?

Appreciate any insights. Thanks!

3 Answers

/Volumes is where all your external disks are mounted.  DO NOT try to get rid of it.  The /Volumes folder does not use much storage, and when an external disk, network attached storage, or a disk image is mounted in the /Volumes folder the storage is on another device or in a disk image.


Starting with Catalina, macOS was separated into a read-only volume and a read/write volume (the iMac - Data).


The read-only volume contains all the macOS programs, libraries, fonts, etc...  This way it difficult to hack and insert malware.


The Read/Write volume is where your files go, preference files, config files, macOS logs, caches, etc...


The mirror folders are a macOS file system abstract concept called synthetic links (man synthetic), which allows macOS to marry a read-only folder and a read/write folder to make it look like there is only one.  Sometimes they are referred to a firmlinks.   synthetic links are also a way for users to create the appearance of a folder on the read-only volume, but in reality the folder is on a read/write volume.


DO NOT delete any of these folders or files either.


Besides better security, another reason macOS went with a read-only and read/write volume split was to keep users from destroying their macOS operating system setup, and then crying to Apple Support that their Mac is broken.


SO DO NOT attempt to get rid of these hidden files.  If you succeed, I strongly suggest you have a really good back so you can restore a working macOS with all your data.

This post was modified 4 weeks ago 2 times by datafornothinandbitsforfree

Thanks, Yeah, I wondered if it had anything to do with these "new" split volumes. But I am still confused. The Finder says that there is 2.5 TB of data on my 3 TB drive. But that seems to include the 1 TB that /Volumes takes up. Is that "real" data that takes real space? If I were to get a 2 TB external SSD, would all my data fit on that drive? Or would I need a 3 TB SSD? I think that I understand there may be some caching (not sure that is the right word) with the firmlinks and all, but a 1 TB /Volumes folder seems a bit much.

And Daisy Disk does uncover an item that is hidden called "other volumes" that is 9.8 GB.


If you are using Time Machine as a backup, then the recommended size is 3 times the amount of space you want to backup, so that you have ample room to keep older copies and thus go back in time several months (even years) to older copies of a file.


If you are just going to make a clone, then you need a backup devices that is at least as large as the amount of data you current have.


As to 'other volumes' I do not know every hidden file on macOS.  But I would again caution you to be careful about deleting files are are not in your home folder, and even in your home folder, I would be very careful about deleting things in your home folder -> Library subfolder, as the Library subfolder has things like your email, iPhone backups, preferences, Notes, etc...

I am actually not looking to use an external drive as a backup (already have two, one TM and one CCC clone) but rather thinking of moving entirely to an external SSD for performance reasons.

This is all so confusing, so I keep digging. There are several of these "volumes" folders in the new APFS/split drive configuration:
and "other volumes" under "hidden space" (in Daisy Disk)

My main reason in trying to understand all this remains to understand if the 1 TB /Volumes is:
1. real files taking up real space, and
2. normal for a drive with 1.5 TB of data


For performance, mostly you need the SSD to hold the operating system, the applications, and it would be good to hold the non-huge items from your home folder.


iTunes, Photos, iMovie can all point to another device for the big stuff.   There are webpages with instructions on moving these library to another device, and getting the apps to look on that device for the content.


If you have huge file content that is not managed by an app with the ability to point to an external device, you would figure this out based on the app that uses those files.


So you could most likely get away with a 512GB or 1TB SSD for the boot device, and then keep all the bulk storage on the Fusion drive.


If you do not want to deal with splitting your files into 2 different devices, then get a 3TB (or larger SSD) and use something like Carbon Copy Cloner to move your bootable system to the new external SSD.


If in your Daisy Disk explorations, you have found files in you home folder that are wasting space, then by all means free that space up, as long as you know it is a file you created, or downloaded, and no longer need it anymore.


And DO NOT assume that if the file is on Time Machine you can delete it.  Time Machine is a backup of your current files.  It is not an archive, even if it will keep old copies.  Eventually Time Machine will delete old copies when they age out several months.