Cannot install Sequoia on external SSD

So you were never able to install macOS onto an external drive five months ago?

This appears to be the most recent thread from 5 months ago:

Cannot install Sequoia on external SSD -- @NowApple - Apple Community

However, it seems you've had multiple threads regarding macOS install issues:

Search - @NowApple "install external" -- Apple Community

Have you tried booting into Safe Mode to install macOS? This will bypass most of the third party software that will interfere with the normal operation of macOS, but not all.

Have you ever tried creating & using a bootable macOS USB installer?

Create a bootable installer for macOS - Apple Support

I suspect your external SSD may be the problem. I've never heard of that brand of SSD. I do know that Macs are very particular about the drives used for booting. Have you ever tried using another brand of SSD?

I would even try using a high quality USB-C cable from a respected brand as well since the cables provide by the drive manufacturers are not always of the best quality (a boot drive requires better quality cables than a data only drive because large amounts data must be transmitted in two directions when used as a boot drive).

You can also try a DFU Firmware Revive which resets the security enclave & system firmware. This should not affect the data on the internal SSD, but I don't know what may happen if the process does not complete successfully. If the Revive doesn't work, then you could try a DFU Firmware Restore which may update the system firmware and also resets the internal SSD destroying all data on it & pushes a clean copy of macOS onto the internal SSD. You will need to restore from a backup with the DFU Firmware Restore option.

How to revive or restore Mac firmware - Apple Support

FYI, just for general reference, here is an Apple article with instructions for installing macOS to an external drive:

Install macOS on an external storage device and use it as a startup disk - Apple Support

NowApple wrote:

Have you tried booting into Safe Mode to install macOS? This will bypass most of the third party software that will interfere with the normal operation of macOS, but not all.

Well, as mentioned I did from Recovery Mode•

Yes, but Recovery Mode can have its own issues for many people. Even with using Recovery Mode there can be issues when rebooting for phase 2 of the installation process.....entering Safe Mode at this point can make a difference.

Should be this even better?

Have you ever tried creating & using a bootable macOS USB installer?

Create a bootable installer for macOS - Apple Support

Yes, I did and just followed the instructions from that link

It keeps everything local and gets rid of all the possible network issues related to Recovery Mode. Plus it helps provide more information to us.

Actually I also used SANDISK UBS RAM key (32GB and 64 GB), they did not work either.

USB sticks are not recommended because they tend to be very slow (at least for writing to them) and they are also not very reliable or of great quality. Granted the SanDisk USB sticks are of much better quality than most, but they can still be a problem since they appear as a USB stick many times instead of an SSD....this in itself can cause problems especially for booting.

Apple hardware & macOS itself are not very forgiving & are very particular about the drives used....especially for booting.

At what point in the installation process do you get the error?

Keep in mind the M-series Macs have a new concept of ownership. The M-series secure enclave chip controls everything and it is possible the information related to existing user accounts & system ownership is corrupted. I've definitely seen issues with the secure enclave getting confused on the T2 Intel Macs, so it would not surprise me if the M-series has some issues as well. This is why I suggested the DFU Firmware Revive & Restore options.

If you have at least 80GB-100GB of Free storage space on the internal SSD, then you could try installing macOS onto a new APFS volume alongside the existing macOS installation (it is a "minor" change to the drive layout, but doesn't resize or relocate anything...very quick & easy to create a new APFS volume). This would at least eliminate the external drive & cables & any other external booting issues. Ignore the "Available" storage value shown everywhere within macOS since it is very misleading......"Available" is not synonymous with Free in macOS. Unfortunately the Free storage value is only shown in Disk Utility. You probably won't be able to migrate anything to this installation, but it is just about figuring out the macOS installation issues. If you cannot install to the internal SSD, then I think the DFU Firmware Revive or Restore are your only options.

NowApple wrote:

HWTech wrote:

I've given you my best guesses to resolving the problem with the information you've provided us here. Apple doesn't provide much information about the "personalization" issue or even "ownership". These are all new concepts to the M-series Macs. If we can uncover some reliable information or better yet actual Apple documentation about "personalization", it would help, but I haven't seen or found anything useful when I searched previously.

I think I know what you are saying here, I used to provide my little helps too when I could, and it is pity.

I actually stumbled across a reference to "personalization" the other day while looking through some macOS command line documentation. It was only a line or two, but at the moment cannot recall where I saw it. I wanted to go back to it since I knew there was a thread here where "personalization" was mentioned. I'll see if I can remember to look for it again hopefully remembering this thread as well.

I always used to test the new Mac OS version on external disk before moving from the old version to the newest, though this is starting to be very difficult to be accomplished easily as it was.

Yes, it has become more difficult & complicated, but still possible for now. Here is an Apple article with instructions for installing macOS onto an external SSD:

How to use an external storage device as a Mac startup disk - Apple Support

The most critical part of that article for an M-series Mac is not using the DFU Port during the installation of macOS to the external SSD. Identifying the DFU Port is the next difficult part since Apple has decided not to standardize on the placement of the DFU Port or marking it as such on the device. The Apple documentation to identify the DFU Port is even more confusing by how it is written....it's like the Albert & Costello's "who's on first" routine.

Just know that making bootable clones is a thing of the past which should be avoided. The best you can do is install macOS to an external SSD & use CCC or SD to sync your data to the external drive.

You said your boot drive was almost full . . . how full?

What is its size and how many GBs are on it? How many gigabytes are free?

Anything less than 10% and you are asking for trouble.

You may be formatting your external disk incorrectly.

Open Disk Utility and select View/Show all devices.

Make sure that you select the external SSD's Physical Disk and not Volume.

Like this . . .

NOT LIKE THIS. You need to see the word "Disk".

Once you have selected the correct part go ahead and format it.

NowApple wrote:

However, I am still not understanding why it starts to install the macOS on the SSD, and gives the error message after hours of working on the installation phase (I suppose of coping files): what happens? Why it does not stop with the error sooner when it starts to install the macOS?

Perhaps it doesn't try the "personalization" step until later in the install process because things are not yet ready enough for it. I don't know. I also don't know when during the installation process you receive this error. Maybe the installer log would contain a clue, but the installer log can be difficult to read & locate the relevant section since it may contain lots of "normal" error messages.

I've given you my best guesses to resolving the problem with the information you've provided us here. Apple doesn't provide much information about the "personalization" issue or even "ownership". These are all new concepts to the M-series Macs. If we can uncover some reliable information or better yet actual Apple documentation about "personalization", it would help, but I haven't seen or found anything useful when I searched previously.

I have been wanting to install macOS onto an external SSD as an experiment to test out a few things, but I just don't have the time at the moment. Maybe I'll try it one night this week or this weekend since I did recently upgrade one M-series Mac to Tahoe using a 2nd APFS volume (testing purposes & to see if I can stand the new look). I believe I did install macOS to an external drive on an M1 Mac a few years ago (no issues).

Not sure what I said previously but there is one consideration to contend: firmware installation with betas. I had a M4 Mini running Sequoia and installed Sequoia Beta on an external drive. I booted from the EHD and uipdated Sequoia Beta. That brought with it a firmware update that my public Sequoia on my internal boot drive didn't like and gave the dreaded blinking amber light on the Mini. Couldn't boot normally or at all after that.

Had to take the Mini into my Genius Bar (that heavens it's very close) and they quickly erased and reinstalled Sequoia public on the boot drive. I then had to take it home and use Migration Assistant to move my apps and user data from my latest Time Machine backup.

So be warned about the possibility of firmware updates and what might happen. Be sure you always have a full and current backup of you MBA.

You might add a link to your original topic in your next post so we can see what was discussed at that time.

NowApple wrote:

My internal boot drive is 500GB

I normally used to have to partitions on my internal disk:

one for the Mac OS, Software and further things like Mail, Calendar, Contacts, Photo, etc.

• one only for my Data like documents and files

•

Then reading something on Apple Support, someone suggested to use Shared partition instead of physical partitions,

Good. With the APFS file system, using multiple APFS volumes is the proper way to do things if you want to physically separate items since the storage pool is shared with all the APFS volumes within a single APFS Container.

I never recommend using multiple partitions because the drive must be physically divided into sections and people usually discover later on that one or both partitions are too small and they must wipe everything to start over again which is a risky & time consuming process.

so I did and now I have:

APPLE SSD AP0512Q Media

• Apple Fabric Internal Physical Disk • GUID Partition Map

It says full (not sure?)

Container disk2

• APFS Container

SHARED BY 6 VOLUMES

Free says zero bytes

Macintosh HD volumes

• APFS Volume Group • APFS

macOS 12.6.7 (21G651)

349.75 GB

SHARED BY 6 VOLUMES

Used: 349.75 GB

Free: 52.17 GB

Notice the Free storage value I have highlighted. This is the most important & accurate/reliable storage value for an APFS volume in macOS, but it is unfortunately only shown in Disk Utility & the System Profiler. The "Available" storage value shown every where else in macOS is very misleading and is not synonymous with Free.

This from diskutil list

/dev/disk0 (internal):

  #:            TYPE NAME          SIZE    IDENTIFIER

  0:   GUID_partition_scheme             500.3 GB  disk0

  1:       Apple_APFS_ISC ⁨⁩            524.3 MB  disk0s1

  2:         Apple_APFS ⁨Container disk2⁩     499.8 GB  disk0s2

/dev/disk2 (synthesized):

  #:            TYPE NAME          SIZE    IDENTIFIER

  0:   APFS Container Scheme -           +499.8 GB  disk2

                 Physical Store disk0s2

  1:        APFS Volume ⁨Macintosh HD - Data⁩   271.1 GB  disk2s1

  2:        APFS Volume ⁨Macintosh HD⁩      15.4 GB  disk2s3

  3:       APFS Snapshot ⁨com.apple.os.update-...⁩ 15.4 GB  disk2s3s1

  4:        APFS Volume ⁨Preboot⁩         726.9 MB  disk2s4

  5:        APFS Volume ⁨Recovery⁩        1.6 GB   disk2s5

  6:        APFS Volume ⁨VM⁩           8.6 GB   disk2s6

  7:        APFS Volume ⁨MYDATASPACE          150.0 GB  disk2s7

What is that APFS Snapshot ⁨com.apple.os.update? Can I delete it?

No, that is part of the macOS system volume. It usually contains the staging area for the macOS updates, or possibly even the existing system volume. It can depend on the version of macOS involved since Apple has been making lots of changes it ever since Catalina.

What is that 8.6GB as Volume VM?

Virtual Memory aka the system Swap "partition". When the system memory is full, macOS will start swapping out currently unused areas to the drive. This is that portion of the drive.

I would never use a shared partition again, it is very confusing, although this is not the issue now

Do you mean the traditional partition or the APFS volumes which share a single Container & storage pool?

These APFS volumes act just like the old style partitions, but do not require hard segmentation of the drive to specific sizes although you can specify an APFS volume to be restricted to a specific size (aka Quota). You can add & delete an APFS volume with no risk of destroying the entire drive or the data on it, unlike modifying traditional partitions which usually require erasing the drive (assuming you don't delete the wrong volume & you have good backups as well).

The data in each APFS volume is completely separate from each of the other APFS volumes. You can even individually encrypt any or all of the APFS volumes you create.

Avoid traditional partitions at all costs. If you want to separate things, then use APFS volumes or purchase multiple drives to achieve the goal, otherwise you are likely to need to wipe the drive & start over when you realize one or more of those partitions is too small. Why risk it? It is your system, so feel free to do as you wish. I can only offer advice for you to consider.