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Replacing Ventura Fusion drive with SSD fails

A1419 Mid-2017 27” iMac i5, 64GB RAM, 1.3GB Fusion drive (1TB HDD + 32GB SSD), running Ventura 13.4.


In an effort to eliminate beachballs and speed operation, cloned Fusion drive to a single, newly formatted (Ventura) 2TB Samsung SSD. Copy completed with no errors. (Also made full copy on a spare 1TB SSD.)

Connect new 2TB SSD via USB to a brand-new M2 MacMini running latest Ventura 13.4.1 (with Startup Security Utility set to “reduced”). Ran Disk Utility on format, wrapper and directory, all 3 verified correctly, code 0, no problems found. (External drive not available as startup, BTW.)


The iMac refuses to recognize the new 2TB SSD, internal or external. Produces blinking question mark.

Installed drive to the iMac anyway. Reset PRAM, no change, using wired keyboard/mouse.

Running online recovery from iMac: Disk Utility produces Code 8 errors all around.

Connected target disk mode to Mac Mini, drive mounts and verifies correctly as before.

Taking iMac back to online recovery, the reinstall OS option produces installer for OS Sierra, 10.12. Might explain online recovery’s Disk Utility failures.

Tried “online help” to download Ventura. Found it on App Store. Apple’s get button goes to an ad for the 15” MacBook Pro. No OS. Then it says browser is out of date.( iMac has 13.4 Ventura, running from online Recovery.)


Went back to the MacMini, downloaded latest Ventura 13.4.1 installer using MacMini to the iMac's SSD.

Attempt install = error, “Downloading the installer build manifest failed” with OK button. 

Copied installer to MacMini, attempt install to iMac failed with, “you may not install to this volume because it is in target disk mode” with OK button.

Removed 2TB SSD from iMac, connected it via USB, mount = OK. Tried running installer from new 2TB SSD again = “The recovery server could not be contacted” with OK button.

Tried installer from MacMini to the iMac = “Downloading the installer build manifest failed” with OK button. 


So now I’m stuck. Startup goes straight to online recovery, and online recovery wants to go back to Sierra 10.12.

I have little faith in TimeMachine backup, but there is a one - if I can find it - will try that next.

Meanwhile, if anybody has some magic to obtain Apple’s blessing for this relatively simple upgrade, any/all suggestions would be gratefully received. Thanks.



iMac, macOS 10.13

Posted on Jul 3, 2023 6:26 PM

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Posted on Jul 3, 2023 7:55 PM

(with Startup Security Utility set to “reduced”).

Why? You don't need to reduce security to boot from an external drive. Just enable booting from an external drive.

(External drive not available as startup, BTW.)

A clone's not a clone anymore.

The iMac refuses to recognize the new 2TB SSD, internal or external. Produces blinking question mark.

That would indicate it's not really a valid startup drive.

Installed drive to the iMac anyway. Reset PRAM, no change, using wired keyboard/mouse.
Running online recovery from iMac: Disk Utility produces Code 8 errors all around.
Connected target disk mode to Mac Mini, drive mounts and verifies correctly as before.
Taking iMac back to online recovery, the reinstall OS option produces installer for OS Sierra, 10.12.

You may have to install Sierra, then upgrade. Once upgraded, Migrate from your Time Machine backup.

I have little faith in TimeMachine backup, but there is a one - if I can find it - will try that next.

Is there a reason you can't make a backup, now? Did you start all of this without a current backup? Maybe get another drive and use the clone you made to migrate from. No idea if that will work, though. I guess if you pulled the two drives, they may not be fused anymore.

Meanwhile, if anybody has some magic to obtain Apple’s blessing for this relatively simple upgrade, any/all suggestions would be gratefully received. Thanks.

It is simple. You tried to make it difficult by cloning Ventura. That's not simple anymore.

With a valid Time Machine backup, install a bare SSD, Install whatever OS it offers, upgrade, Migrate. If you can't install Ventura straight away, create a user that does not share the same name as the ones you wish to migrate later.

Instead of installing Sierra and upgrading, create a bootable installer for Ventura on that Mac

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14 replies
Question marked as Top-ranking reply

Jul 3, 2023 7:55 PM in response to Motorcycle Michael

(with Startup Security Utility set to “reduced”).

Why? You don't need to reduce security to boot from an external drive. Just enable booting from an external drive.

(External drive not available as startup, BTW.)

A clone's not a clone anymore.

The iMac refuses to recognize the new 2TB SSD, internal or external. Produces blinking question mark.

That would indicate it's not really a valid startup drive.

Installed drive to the iMac anyway. Reset PRAM, no change, using wired keyboard/mouse.
Running online recovery from iMac: Disk Utility produces Code 8 errors all around.
Connected target disk mode to Mac Mini, drive mounts and verifies correctly as before.
Taking iMac back to online recovery, the reinstall OS option produces installer for OS Sierra, 10.12.

You may have to install Sierra, then upgrade. Once upgraded, Migrate from your Time Machine backup.

I have little faith in TimeMachine backup, but there is a one - if I can find it - will try that next.

Is there a reason you can't make a backup, now? Did you start all of this without a current backup? Maybe get another drive and use the clone you made to migrate from. No idea if that will work, though. I guess if you pulled the two drives, they may not be fused anymore.

Meanwhile, if anybody has some magic to obtain Apple’s blessing for this relatively simple upgrade, any/all suggestions would be gratefully received. Thanks.

It is simple. You tried to make it difficult by cloning Ventura. That's not simple anymore.

With a valid Time Machine backup, install a bare SSD, Install whatever OS it offers, upgrade, Migrate. If you can't install Ventura straight away, create a user that does not share the same name as the ones you wish to migrate later.

Instead of installing Sierra and upgrading, create a bootable installer for Ventura on that Mac

Jul 6, 2023 7:37 PM in response to Barney-15E

Time Machine drives have been bootable since - what, 10.13 High Sierra? Startup security won't allow it, nor is TM drive recognized. Even if it was, I can't use it to restore, only to migrate after Ventura is installed.


Did make some progress, tho. Put a Mojave SSD into machine, and Startup Manager is back! iMac boots up, external drives are available (might startup to an internal Catalina or Monterey drive, too). And, the Time Machine drive now mounts (USB). Had to try Restore from Mojave's (onboard) recovery partition, got this:



So, no good, Cancel.

Upgraded to Catalina, and that may be where this iMac stays. At least I can drag/drop from the backup(s) now, and upgrade later. Plus, Recovery is on the drive instead of online. (Online Recovery needs to be fixed.)


Thank you one and all for suggestions and solutions. Downloading six Operating Systems on a 2Mbps line is a career path I'm happy to avoid, but might be only choice for some. Would still like to disable Startup Security on the Mini - having options is preferable to unnecessary security measures.

Thanks again!


Jul 3, 2023 7:15 PM in response to Motorcycle Michael

You can’t clone any recent version of macOS. You would need to erase the external drive, download the OS installer, and select the external as the target for installation. Then you could copy your data using Migration Assistant or similar.


However, you may not notice very much improvement. An external SSD is going to be limited by your (probably USB) bus. Thunderbolt would be much better, but those are hard to find.


If the mechanical part of your Fusion Drive is failing or just spectacularly slow, as some of them are, then the above may not apply. In those cases, even a clunky USB SSD can be better. But if this is the case, I recommend that you erase both the internal SSD and HDD portions and don’t use them. Even having any data on the HDD could slow down the system.

Jul 3, 2023 8:27 PM in response to etresoft

I have done what Barney suggests and can attest that it does work.


"... install a bare SSD, Install whatever OS it offers, upgrade, Migrate. If you can't install Ventura straight away, create a user that does not share the same name as the ones you wish to migrate later."


I offer up our late 2015 iMac, originally shipped with 10.11, El Capitan, had been running High Sierra but with a slow HDD. El Capitan (10.11) is what is installed by Internet Recovery on a new bare SSD, which we installed to replace the original HDD. I then upgraded to 10.12 Sierra, then 10.13 High Sierra, then 10.15 Catalina (skipped Mojave), then Monterey 12.6.7 (skipped Big Sur). This is the highest MacOS for this iMac. It sounds laborious but once you start plowing through these MacOS versions, it goes fast, and very smoothly, especially with a good internet connection and an SSD inside. Maybe a few hours. Since the machine is basically factory bare, there are no complications, and as we did this we had a single administrator user called ADMIN. After reaching the final MacOS 12.6.7 (Monterey), I then ran Migration Assistant on the Time Machine backup previously made from a much older MacOS migrating over ONLY accounts and files but no settings and no software.


This is basically what Barney suggests (except your iMac is newer and can go to Ventura, mine stopped at Monterey).


This is a very smooth and trouble free way to quickly get to the final MacOS from a bare, new internal SSD. No fuss with an external drive Ventura installer (which should work also but this other method just requires one session with internet recovery, followed by simply selecting Software Update and clicking "install" several times).



Jul 6, 2023 12:12 PM in response to Barney-15E

"It is simple. You tried to make it difficult by cloning Ventura."


Well.... given all of the above, how does one replace a Ventura Fusion drive (32GB SSD + 1TB HDD, APFS)?

Startup Manager is gone, Target Disk Mode can't be used, and online Recovery is all 10.12 Sierra only.

Online Recovery cannot find its own (current and complete) Time Machine backup files. There are seven.


Because online Recovery only sees 10.12 Sierra, Disk Utility puts up false errors, reinstall OS = Sierra only, and restore from Time Machine fails. All instructions to a dead end.

Is there a Terminal command to shut off Startup Security entirely? Would TM then be able to restore?

Jul 7, 2023 10:34 AM in response to Barney-15E

Wait - what?! Time Machine no longer makes a FULL backup? Sure enough, you're right again (and about TM not being bootable, tho I'd swear I did that once long ago). Wow, no onboard Recovery partition, no OS backup - what's the point of using TM then? Thank you for the heads-up.


iMac is going up to Monterey, as recommended by a key application, and will stop there. Then I get to extract whatever I can from the (clone) backup of Ventura. Beginning to wonder if these machines work for us, or we work for them.... Will call this solved - thanks.

Jul 11, 2023 8:28 PM in response to Barney-15E

Misinformation? I must be onto something ;-)

Time Machine has lost its key feature, namely the ability to copy or restore a bootable volume. The clone apps (apparently) are no longer capable of creating a bootable backup either - far as I know. Bear in mind, there was no problem with the Fusion drive other than being intolerably slow due to a tiny SSD + APFS HDD.


Happy to report that once the Ventura drive was removed and an internal drive with Mojave on it was installed, machine's operation returned to normal regarding external drives. No need to download Sierra and work thru upgrades. (I suspect Catalina would've worked as Mojave did, maybe even Monterey, tho I did not test either.)


We put Monterey on the new 2TB SSD after reformat, then discovered that migration from 1TB Ventura clone into Monterey worked flawlessly - all without 6-8hour downloads thru online Recovery (which only allowed Sierra). Thru all this, the Time Machine backup proved to be useless (since reformatted to Monterey).


Jul 12, 2023 5:36 AM in response to Motorcycle Michael

Motorcycle Michael wrote:

Time Machine has lost its key feature, namely the ability to copy or restore a bootable volume.

This was never a feature of Time Machine. I have seen innumerable fights over Time Machine vs. cloning tools over the years. I can assure you that Time Machine never, ever did that.


At one point, Time Machine did include its own Recovery volume, thereby making it "bootable". But again, I can assure you that no proponents of cloning tools ever accepted this capability as 1) actually being bootable, 2) actually existing at all, or 3) ever having been typed in the online dispute. On the rare occasions that they did acknowledge the fact, it was irreverent because it wasn't absolutely instantaneous like a cloning tool, thus making it unsuitable for restoring a Mac from backup, which had to be done at least 4 times each week.


I honestly don't know if the current version of Time Machine still includes a recovery volume. It turned out that in 20 years of those pointless fights, I've never once needed to boot from the Time Machine recovery volume. Given the secure boot requirement of recent Macs, it seems logical that this is now a moot point. It makes sense to have removed this feature.

there was no problem with the Fusion drive other than being intolerably slow due to a tiny SSD + APFS HDD.

If your Fusion Drive was intolerably slow, then there was most definitely a problem with it. But you didn't ask about that. You asked about cloning. As far as I can tell, you haven't even tried setting up the external as a boot device.

We put Monterey on the new 2TB SSD after reformat, then discovered that migration from 1TB Ventura clone into Monterey worked flawlessly - all without 6-8hour downloads thru online Recovery (which only allowed Sierra). Thru all this, the Time Machine backup proved to be useless (since reformatted to Monterey).

You can't restore to a previous operating system. You can erase the hard drive and restore the old version. But any apps, especially Apple apps, are going to be totally confused. If it works at all you will be plagued by odd problems forever.

Jul 12, 2023 5:54 AM in response to Motorcycle Michael

Misinformation? I must be onto something ;-)
Time Machine has lost its key feature, namely the ability to copy or restore a bootable volume.

Making a bootable backup was never a feature, much less a "key" feature. Backing up the OS was a feature of Time Machine when it was possible, but it certainly wasn't a "key" feature. Backing up your data was the only "key" feature of Time Machine.

Jul 12, 2023 11:16 AM in response to etresoft

You can't restore to a previous operating system. You can erase the hard drive and restore the old version. But any apps, especially Apple apps, are going to be totally confused. If it works at all you will be plagued by odd problems forever.

100% agree, you can't go backwards and migrate from a newer OS (Ventura) into an older one (Monterey). Normally I'd never even try. But, having two backups and nothing to lose, gave it a shot. Surprised when it started, amazed that it completed properly. We went thru apps, checked network and settings, libraries, online ops, photos, files, everything wound up intact and fully functional. Plus, iMac runs fast on Monterey from properly formatted APFS 2TB SSD. No issues. None. Wouldn't believe it if I hadn't seen it. In this case, it worked.


Time Machine has always restored fully functional startup volumes that are identical to selected backup - until recently. I've used TM to restore OS/all to many new drives following drive failure over the years. If TM no longer copies the OS (for security reasons), I'd call that a key feature gone missing.


Worse: If clone apps can no longer copy/restore OS either, then having a backup is no better than using cloud backup - which is barely better than nothing. Unacceptable.


Finally, let me point out that not all of us have access to blazing-fast fiber optic internet. The idea of having to download a behemoth OS taking six hours or more every time there's a drive failure is also unacceptable.

Jul 12, 2023 12:57 PM in response to Motorcycle Michael

If I may, Carbon Copy Cloner has made tremendous strides in creating a "Bootable System" to be pretty reliable in doing so. I have 3 drives all 1TB, a Samsung 860 EVO SSD internal, and 2 Western Digital 1TB NVME's connected via Thunderbolt, all of which are bootable. I've tried all 3 with success, numerous times in testing the viability of "Bootable" backups or Migrating on a new OS successfully, yes AppleID is asking for passwords, Carbon Copy Cloner is warning that you're booting off a "Backup" and having you "review" all your scripts (Tasks) and the "normal" routine when installing a new OS, a "Bootable" backup or Migrating. So ultimately it works at least for me at or near 100% of the time.

I've been using CCC since High Sierra on a 2011, 2015 iMac and now a 2019 iMac, and rarely (I can't recall a time, but people freak out at 100% ) has it failed in creating a bootable volume, whatever OS.

I run my iMac off of an external NVME, substantially faster than the internal SSD.


2019 iMac 19, Ventura 13.4.1

3.7 GHz

64 GB of RAM

Sys Firmware 1968.120.12.0.0

I hope this helps with a "Bootable" Volume.

Replacing Ventura Fusion drive with SSD fails

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