Monterey external SSD questions


I’m currently running Mojave on my 2019 iMac. I purchased an SSD drive to install Monterey on, just to acquaint myself with the newer system. I’m still primarily going to continue to use Mojave for now.
I prepared the SSD by naming it Monterey and formatted it APFS & GUID Partition Map.

When I installed Monterey on the external drive I used Migration Assistant to an extent, but - not anticipating any issues - I did not make note of what I migrated other than I definitley unchecked Applications, and I did check Other files and folders, as well as Computer Network and settings.
After booting into Monterey and briefly taking a glance around, I rebooted back to Mojave. My questions are:

  1. When booted back to Mojave, my Monterey drive is shown on the desktop as: Monterey - Data. I’m wondering why would this be?

  2. Also, now appearing on the Mojave desktop is an ejectable disk named Update, with some various files and folders in it.

  3. Looking at Disk Utility the Monterey disk is shown as:
    Samsung PSSD T7 Media (USB External Physical Disk - Guid Partition Map)
    Container disk5 (APFS container)
    Monterey - Data (APFS Volume (APFS)
    Update (APFS Volume (APFS)

I’m not sure what I did wrong. As I was doing this install out of curiosity, I have no issues if I have to erase the drive and start over.

These days a Mac’s boot partition is actually split up into two. One contains the system and is mounted when booted from it as read-only, the other is called Data and is essentially your docs, your apps, and a few parts of macOS (such as Safari). During use, the two partitions are fused so the user doesn’t notice, but the one you actually interact with is the Data partition. When you boot back into Mojave, what you’re seeing is your external disk, except not all of it. What Finder is showing you is the Data partition.

Hi Simon -
Thank you for your response. I’m still a newbie when it comes to understanding the volumes / containers system as it is these days. Actually, now that I think of it - since owning this iMac for the last few years I’ve never had any need to boot to another drive - not even the clone that I keep - so the sudden appearances of these disks kind of startled me. From your description, it appears to be normal behavior and not something I did wrong?

I don’t see anything acutely wrong here. Although I must admit, I have never seen what a Monterey install looks like as seen from Mojave.

Catalina was the first version of macOS that split up the boot partition into System and Data (and the SSV was only introduced with Big Sur), so I would not be surprised to see Mojave display these things a bit different from what later versions of macOS would.

Thank you for reassuring me about it Simon. I was actually thinking of installing Catalina, but figured if I’m not risking too much by installing on a separate disk, I might as well head straight to Monterey. Thanks again!

You might find this article of interest:


Thank you David - I’ll give that a read in the morning. Very much appreciated!

I did exactly what you are doing, with 2018 iMac running Mojave. Installed first on external SSD to see what it looks like, migrating just a few apps . All good so I Then installed Monterey directly to my iMac via software update. Again, very smooth, no hiccups. Unlike some others on this list, it installed without hours of delay. I had previously done the cleanup via terminal described here Explanation for some Big Sur upgrade problems.

Greetings Tina,
When you first installed on the external drive, when you booted back to Mojave, did you have the same scenario, where your Monterey SSD had “-Data” appended to it’s name, and in addition, another disk called Update? I’m still trying to understand disk containers, but it’s difficult stuff for me. David C. sent me some links as well, but most of it is way out of my grasp. If I did not have some older software I still want to keep running, I would do what you did - just install directly over Mojave (after backing up first of course). I’m also in the process of determining what software I can re-install on Mojave at no extra cost versus which apps I will have to pay for upgrades on.

Hi Jim,
I knew to expect the new volumes and just ignore them. I have kept a bootable clone of my Mojave drive to access old software should I need to in the future. It all has gone more smoothly than I thought it would. :sunglasses:

David -
I tried to read the article and study the the layouts, but I’m afraid the newer Mac OS leaves me very confused. I also happened to come across your comments in the Boot disk layout in macOS Monterey article also. It’s very difficult for me to grasp. I just don’t get why the external drive is not shown as I named it “Monterey” even in the disk utility sidebar. And what is the Update container for? If this is normal behavior because of my specific scenario of having Mojave on one drive and Monterey on another, that’s fine I can deal with that. I guess because of my limited understanding of the newer OS, I just keep thinking I did something wrong during the install.

I’m glad all went well for you with the update. As I was not expecting anything more than a disk on my desktop called Monterey, I thought I did something wrong in the process, being as I did not choose a full-blown migration during the procedure - it’s been so long since I did an install I forgot how much info I was going to have to input - I barely remembered my iCloud password! Anyway, if the 2 containers are a proper result of Monterey being on an external drive, I can live with that and ignore them as you do. Thank you for your help!

Let me see if I can explain.

Ever since Catalina, the boot disk for a Mac is not what you see in the Finder (or even at command-line sessions).

The boot disk actually consists of two volumes - a System volume and a Data volume. On Big Sur and later, the actual System volume is hidden - macOS instead creates a snapshot of it and generates a cryptographic signature for the snapshot in order to make sure it never gets altered.

The System volume is read-only and can only be modified by Apple’s macOS installers. It contains all of the things that should never change without an OS upgrade.

The Data volume contains everything else. This includes most of your apps, all user home directories, device drivers (including kernel extensions) you may have installed, etc.

At system startup, the System volume (or its cryptographically-signed snapshot, the “SSV”) is merged with the Data volume to present one single virtual storage volume to you and your applications. Aside from getting some inexplicable errors if you try to modify a file on the System volume, you shouldn’t normally see the difference.

(The APFS container holding the System and Data volumes has a few other volumes - Preboot, Recovery and VM, but they are purely for internal use. The preboot and recovery volumes aren’t even mounted most of the time. You can safely ignore them).

There should be something like this on your external drive as well. One APFS container holding five volumes - two of which are combined to form the volume you and your applications see.

As for the name that appears in Disk Utility, that’s the internal name of the volumes and containers. It doesn’t necessarily match the name shown in the Finder as the mounted volume’s icon, because the mounted “volume” is actually composed of two internal volumes. Renaming it from the Finder may not push that name into the underlying volumes - because there’s no particular reason why it has to.

I don’t know about the “Update” container you’re referring to. Howard Oakley’s articles don’t show one. They show an Update volume belonging to the Apple_APFS_Recovery container (only present on an M1 Mac’s internal storage device). Is what what you’re seeing or is it something else?

I wouldn’t worry about if anything broke. If the system is running and working, then I wouldn’t worry about it. If you want to try and understand what’s going on under the covers, it might be interesting, but it is complex and unusual so don’t assume anything is broken just because it doesn’t look like what you were expecting to see.

If you want, feel free to open a terminal window and type the following two commands and share with us the output:

diskutil list
diskutil apfs list

These two commands will show you the various containers and volumes that your system has. We may be able to help explain what you’re seeing based on that information.


You named it Monterey and when Monterey was installed it got renamed to Monterey - Data. That is the way macOS does things these days. It’s only confusing because the older macOS Mojave is showing it to you that way. In Monterey you’d be seeing it called what you named it.

Yes, I’m starting to understand that now…I have never performed an install on a separate drive before - much less one as complex as Monterey. Thank you for clarifying.

It’s the same thing for me as I’m on Catalina and when I boot into my Mojave partition, I see two drives for the Catalina partition and the second one has the Data specification. As others have stated, this started with Catalina and it sounds like you did everything correctly. Since my Mac Mini 2012 is limited to Catalina, I can only run Monterey in a virtual machine if need be which is OK for basic use.

You are very gracious in going above and beyond explaining this to me…it’s actually starting to make a bit more sense to me now. I’m new to this discussion board, so I’m interested in taking you up on your offer to post the 2 lists you mentioned, but I’m not sure how to do that properly here. I copied them into rtf documents, but I’m not sure if I would upload those, or just paste the results from the terminal directly into a new reply window? I also made a screen capture showing the contents of the Update container, and a screen capture of the volumes shown mounted in the disk utility sidebar to go along with the diskutil list. Just let me know the best way to post and if you want the screen grabs also. Thanks.
P.S. - this is not urgent, so whenever it’s convenient for you. Thanks again!

To send us the results of these commands, open the Terminal application (it’s in the Utilities folder, in the Applications folder).

Type each command to see the output.

To share it here, just copy the output you get in Terminal and paste it into the TidBITS Talk edit box along with anything else you’d like to say.

To make it look nice, you should put four tilde characters (~~~~) on a line by themselves immediately above and below the output. This tells the system to render all the lines in between in a fixed-width font, and with scroll-bars if it is too big to fit comfortably when people are reading it.

To share a screen-capture, just drag the screen shot image to the editor window. The TidBITS Talk editor will download it from you and automatically insert the special code needed to let it appear. If it’s not in the right place, you can cut/paste the generated code to another part of your message.

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Here are the results - hope this looks right:

JimDs-iMac-2:~ jimd57$ diskutil list
/dev/disk0 (internal):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                         1.0 TB     disk0
   1:                        EFI EFI                     314.6 MB   disk0s1
   2:                 Apple_APFS Container disk1         1.0 TB     disk0s2

/dev/disk1 (synthesized):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      APFS Container Scheme -                      +1.0 TB     disk1
                                 Physical Store disk0s2
   1:                APFS Volume Macintosh HD            267.6 GB   disk1s1
   2:                APFS Volume Preboot                 44.5 MB    disk1s2
   3:                APFS Volume Recovery                510.6 MB   disk1s3
   4:                APFS Volume VM                      3.2 GB     disk1s4

/dev/disk2 (external, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *4.0 TB     disk2
   1:                        EFI EFI                     209.7 MB   disk2s1
   2:                  Apple_HFS Mojave Clone            4.0 TB     disk2s2
   3:                 Apple_Boot Recovery HD             650.0 MB   disk2s3

/dev/disk3 (external, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *1.0 TB     disk3
   1:                        EFI EFI                     209.7 MB   disk3s1
   2:                 Apple_APFS Container disk5         1000.0 GB  disk3s2

/dev/disk4 (external, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *4.0 TB     disk4
   1:                        EFI EFI                     209.7 MB   disk4s1
   2:                  Apple_HFS Time Tunnel             4.0 TB     disk4s2

/dev/disk5 (synthesized):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      APFS Container Scheme -                      +1000.0 GB  disk5
                                 Physical Store disk3s2
   1:                APFS Volume Monterey - Data         137.2 GB   disk5s1
   2:                APFS Volume Preboot                 271.3 MB   disk5s2
   3:                APFS Volume Recovery                1.1 GB     disk5s3
   4:                APFS Volume                         15.7 GB    disk5s4
   5:                APFS Volume Update                  671.7 KB   disk5s5
   6:                APFS Volume VM                      1.1 MB     disk5s6

/dev/disk7 (external, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *6.0 TB     disk7
   1:                        EFI EFI                     209.7 MB   disk7s1
   2:                  Apple_HFS myTunes                 6.0 TB     disk7s2

JimDs-iMac-2:~ jimd57$ 

JimDs-iMac-2:~ jimd57$ diskutil apfs list
APFS Containers (2 found)
±- Container disk1 76B1F8AC-EA5C-4446-A0A3-6F4636F0FD2F
| ====================================================
| APFS Container Reference: disk1
| Size (Capacity Ceiling): 1000240963584 B (1.0 TB)
| Capacity In Use By Volumes: 271618142208 B (271.6 GB) (27.2% used)
| Capacity Not Allocated: 728622821376 B (728.6 GB) (72.8% free)
| |
| ±< Physical Store disk0s2 AF0F632C-01E6-4499-B783-CF74D1203A75
| | -----------------------------------------------------------
| | APFS Physical Store Disk: disk0s2
| | Size: 1000240963584 B (1.0 TB)
| |
| ±> Volume disk1s1 1DC55CF1-1211-4FB0-906C-E2E4DF967811
| | ---------------------------------------------------
| | APFS Volume Disk (Role): disk1s1 (No specific role)
| | Name: Macintosh HD (Case-insensitive)
| | Mount Point: /
| | Capacity Consumed: 267633958912 B (267.6 GB)
| | FileVault: Yes (Unlocked)
| |
| ±> Volume disk1s2 E49E5963-518E-4EE1-A5CB-6039D3E2035A
| | ---------------------------------------------------
| | APFS Volume Disk (Role): disk1s2 (Preboot)
| | Name: Preboot (Case-insensitive)
| | Mount Point: Not Mounted
| | Capacity Consumed: 44527616 B (44.5 MB)
| | FileVault: No
| |
| ±> Volume disk1s3 40350D23-C62F-4A30-8D0A-9D363A2C7C07
| | ---------------------------------------------------
| | APFS Volume Disk (Role): disk1s3 (Recovery)
| | Name: Recovery (Case-insensitive)
| | Mount Point: Not Mounted
| | Capacity Consumed: 510562304 B (510.6 MB)
| | FileVault: No
| |

±> Volume disk1s4 C48FD628-B65A-4B63-A242-88CEF3F4DC6C
APFS Volume Disk (Role): disk1s4 (VM)
Name: VM (Case-insensitive)
Mount Point: /private/var/vm
Capacity Consumed: 3221245952 B (3.2 GB)
FileVault: No

±- Container disk5 7E23F4BA-D186-4F4D-8536-3ACD8F571E24
APFS Container Reference: disk5
Size (Capacity Ceiling): 999995129856 B (1000.0 GB)
Capacity In Use By Volumes: 154541731840 B (154.5 GB) (15.5% used)
Capacity Not Allocated: 845453398016 B (845.5 GB) (84.5% free)
±< Physical Store disk3s2 C6988EDA-FE2E-4B38-8142-F2D7A4D7820A
| -----------------------------------------------------------
| APFS Physical Store Disk: disk3s2
| Size: 999995129856 B (1000.0 GB)
±> Volume disk5s1 6B8B4219-C093-44A0-9856-09D9EF4D246B
| ---------------------------------------------------
| APFS Volume Disk (Role): disk5s1 (No specific role)
| Name: Monterey - Data (Case-insensitive)
| Mount Point: /Volumes/Monterey - Data
| Capacity Consumed: 137216348160 B (137.2 GB)
| FileVault: No
±> Volume disk5s2 CA9CDA36-EA32-4B2B-81DF-4EB1754EFF2B
| ---------------------------------------------------
| APFS Volume Disk (Role): disk5s2 (Preboot)
| Name: Preboot (Case-insensitive)
| Mount Point: Not Mounted
| Capacity Consumed: 271335424 B (271.3 MB)
| FileVault: No
±> Volume disk5s3 382C86A3-C253-42C5-8C1F-D4EA8B79F159
| ---------------------------------------------------
| APFS Volume Disk (Role): disk5s3 (Recovery)
| Name: Recovery (Case-insensitive)
| Mount Point: Not Mounted
| Capacity Consumed: 1094529024 B (1.1 GB)
| FileVault: No
±> Volume ERROR -69808
| -------------------
| APFS Volume Disk (Role): disk5s4 (System)
| Name: ERROR -69808
| Mount Point: Not Mounted
| Capacity Consumed: 15749959680 B (15.7 GB)
| FileVault: No
±> Volume disk5s5 827804A2-890D-4AF8-8D82-FBB68B286D52
| ---------------------------------------------------
| APFS Volume Disk (Role): disk5s5 (No specific role)
| Name: Update (Case-insensitive)
| Mount Point: /Volumes/Update
| Capacity Consumed: 671744 B (671.7 KB)
| FileVault: No
±> Volume disk5s6 CC11050B-AC45-4180-9801-E49542DD33D5
APFS Volume Disk (Role): disk5s6 (VM)
Name: VM (Case-insensitive)
Mount Point: Not Mounted
Capacity Consumed: 1069056 B (1.1 MB)
FileVault: No
JimDs-iMac-2:~ jimd57$

1 Like

Thanks. Here’s my analysis:

diskutil list output

  • You’ve got 7 devices. Two of them are synthesized - produced from APFS containers. The other five are physical devices
  • /dev/disk0 (your internal device) has an APFS container (/dev/disk1), and that container does not have separate system/data volumes. So this is clearly a boot device for High Sierra or Mojave
  • /dev/disk2 has an HFS+ partition named “Mojave Clone”. I assume that volume is what it says it is
  • /dev/disk3 has an APFS container (/dev/disk5) with your Monterey system. I’ll talk about it more below.
  • /dev/disk4 has an HFS+ volume named “Time Tunnel”. I assume, from the name, that this is a Time Machine volume created prior to Big Sur
  • /dev/disk7 has an HFS+ volume named “myTunes”. Clearly this is external music storage

The interesting part is the content of /dev/disk5 - the APFS container holding your Monterey system. It contains 6 APFS volumes:

  • Monterey - Data. This is the data volume for the system. It will contain most of your apps and all your data
  • Preboot, Recovery, VM - these are all standard volumes.
    • Preboot is used before the OS is loaded. It also provides the initial login screen if the volume is encrypted
    • Recovery is used when you boot into recovery mode
    • VM hold swap files, should you need them
  • The unnamed volume (position 4), looks like it should be the Monterey System volume. It’s about the right size for it (15.7 GB). But I don’t see any accompanying APFS snapshot.
  • A volume named Update. I don’t know what this is. Does it appear on your desktop? Could it be a volume you created? It has very little content (only 671.7 KB)

Is this Monterey disk bootable? Given the absence of a system snapshot, I’m thinking it might not be. If it is, maybe the Update volume is a temporary one that will go away after the system snapshot is created and sealed.

I was expecting to see something like this (from my Big Sur system):

$ diskutil list
/dev/disk1 (synthesized):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      APFS Container Scheme -                      +2.0 TB     disk1
                                 Physical Store disk0s2
   1:                APFS Volume Balrog                  15.3 GB    disk1s1
   2:              APFS Snapshot 15.3 GB    disk1s1s1
   3:                APFS Volume Balrog - Dat            1.1 TB     disk1s2
   4:                APFS Volume Preboot                 376.1 MB   disk1s3
   5:                APFS Volume Recovery                623.4 MB   disk1s4
   6:                APFS Volume VM                      1.1 GB     disk1s5

Note that my system has the snapshot (#2, disk1s1s1) that it actually boots from.

But that’s OK. Let’s dig deeper and look at the diskutil apfs list output.

It is showing two containers. The first container (disk1, based on physical store disk0) is your internal storage device. I’m going to skip over it, because it looks perfectly normal for a pre-Catalina APFS boot device.

The second container (disk5, based on physical store disk3) shows the following volumes:

  • Monterey - Data. This is your data volume. But it says there is “No specific role”. This is wrong. It should have a role of “Data”
  • Preboot. Has a role of “Preboot”, as it should
  • Recovery. Has a role of “Recovery”, as it should
  • That unnamed volume is presenting a name of “ERROR -69808”. That’s bad. It has a role of “System”, as it should. It has no snapshots, which is wrong.
  • The Update volume has no specific role. Since I don’t know what it’s for, I’m going to ignore it
  • The VM volume has a role of “VM” as it should.

It appears to me that your Monterey installation is messed up. If you haven’t started using it yet, I would wipe the entire disk and redo the installation from scratch. If you are using it, see if you can re-run the Monterey installer (maybe after booting the Monterey Recovery disk), so it can reinstall the system while preserving your Data volume.

Looking at the contents of Update, it looks like lots of internal data. I’m guessing that there was an update (or installation) in progress that got interrupted. This volume was probably holding temporary files for use during the update, and they got left behind since it was interrupted.

That interruption might also be what seems to have messed up your Monterey System volume.

So a short answer is: It looks like your Monterey system volume is broken and a reinstallation is probably your best bet at fixing it.