Level 1

13 points

Cannot install Sequoia on external SSD

Sorry for posting again this issue but I did not get through out from this nightmare.

And thanks to all who already tried to provided me some help.

I have been trying to install MacOs on external drive without any success, actually I want to install Sequoia.

The reason is because I use always to test the new mac os version, trying to migrate my data to the new version on the extern drive, but I cannot go further to the same error:

An error occurred preparing the update.

Failed to personalise the software update. Please try again.

My system:

Mac Air M1 2020
Mac OS Monterey 12.6.7
SSD EMTEC 480GB as external USB disk

What I tried:

prepared the external disk keeping the "Shaw all devices" within the DiskUtility
selecting EMTEC X1 50 480GB Media
USB External Physical Disk • GUID Partition Map
single partition as APFS
using the no-DFU port
downloaded installer macOS Monterey
launching installer and followed all the steps selecting the external SSD
also tried to boot from Recovery mode
formatting from there the external drive
installing Monterey from the Recovery mode too
after ages (hours) it showed up the same message (or similar)

This is getting annoying and frustrating.

Please, help if you can.

Many Thanks in advance and ...

THANKS TO ALL THE FELLOWS WHO ALREADY PROVIDED SOME HELP IN MY PREVIOUS POST

Thanks Ian R. Brown

Thanks tbirdvet

Thanks Old Toad

Thanks Owl-53

Thanks Barney-15E

Thanks dialabrain

MacBook Air 13″, macOS 12.6

Posted on Oct 3, 2025 9:27 AM

Top-ranking reply

HWTech

Level 9

68,432 points

Posted on Oct 20, 2025 6:19 PM

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

View in context

21 replies

NowApple Author

Level 1

13 points

Oct 21, 2025 9:53 AM in response to HWTech

HWTech wrote:

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.

I will try this too.

If you have at least 80GB-100GB of Free storage space on the internal SSD, then you could try installing

I have non free - available space on my disk, almost full.

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?

Many Thanks

NowApple Author

Level 1

13 points

Nov 18, 2025 10:58 AM in response to Ian R. Brown

Ian R. Brown wrote:

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.

Well, this is not that easy to say, here the info from Disk Utility....

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, 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

Macintosh HD

APFS System Volume • APFS

macOS 12.6.7 (21G651)

499.75 GB

SHARED BY 6 VOLUMES

Used: 15.42 GB

Free: 52.16 GB

Macintosh HD - Data

APFS Data Volume • APFS

macOS 12.6.7 (21G651)

499.75 GB

SHARED BY 6 VOLUMES

Used: 271.06 GB

Free: 52.16 GB

MYDATASPACE

APFS Volume • APFS

499.75 GB

SHARED BY 6 VOLUMES

(150 GB QUOTA)

Used: 131.12 GB (150 GB reserve)

Free: 18.88 GB

This from diskutil info disk0

Device Identifier: disk0

Device Node: /dev/disk0

Whole: Yes

Part of Whole: disk0

Device / Media Name: APPLE SSD AP0512Q

Volume Name: Not applicable (no file system)

Mounted: Not applicable (no file system)

File System: None

Content (IOContent): GUID_partition_scheme

OS Can Be Installed: No

Media Type: Generic

Protocol: Apple Fabric

SMART Status: Verified

Disk Size: 500.3 GB (500277792768 Bytes) (exactly 977105064 512-Byte-Units)

Device Block Size: 4096 Bytes

Media OS Use Only: No

Media Read-Only: No

Volume Read-Only: Not applicable (no file system)

Device Location: Internal

Removable Media: Fixed

Solid State: Yes

Hardware AES Support: Yes

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?

What is that 8.6GB as Volume VM?

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

Thanks

Please note that I did not tried yet with the installation suggestions received till now, I have really no time, and for this test I need to stop my Mac for hours which means not working for hours.

NowApple Author

Level 1

13 points

Nov 18, 2025 11:09 AM in response to HWTech

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 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.

Thanks for your time and help.

NowApple Author

Level 1

13 points

Oct 20, 2025 11:57 AM in response to NowApple

Any help here please?

HWTech

Level 9

68,432 points

Oct 20, 2025 6:53 PM in response to NowApple

I forgot to ask, do you have Filevault enabled on the internal SSD? This really should not make a difference, but I'm just trying to think of things that could potentially cause a problem.

Old Toad

Level 10

215,196 points

Nov 18, 2025 12:11 PM in response to NowApple

Control (right) - click on your boot drive icon on the Desktop and select Get Info option from the contextual menu. That will tell you how much free space you have on the drive.

You can post a screenshot of the General section of the window.

Cannot install Sequoia on external SSD