User profile for user: Oursamiel
Oursamiel Author
User level: Level 1
4 points

HDD not recongized by mac that was used to format it

HDD with its own external power supply, same USB cable for all steps


Step 1: on a iMac 27'', running 12.7.6 I format a brand new HDD using the AFSP scheme.

All volumes that are created are visible on the finder.


Step 2: move HDD to another old iMac High Sierra, HDD does not mount


Step 3: re-connect on iMac that was used to format the disc, which does not mount anymore. Disk utilisty cannot erase or re-format it. Error.


Step 4: connect HDD on a Mac Book Pro running 10.15.7. Bingo HDD mounts and all volumes are visible.


Thank you for any comment you may provide.

MacBook Pro 15″, macOS 10.15

Posted on Sep 29, 2025 3:24 AM

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User profile for user: MartinR
MartinR
User level: Level 7
24,053 points

Posted on Sep 30, 2025 7:13 AM

Oursamiel wrote:
Step 1: on a iMac 27'', running 12.7.6 I format a brand new HDD using the AFSP scheme.
All volumes that are created are visible on the finder.

Not advisable. A spinning HDD should be formatted as Mac OS Extended (Journaled) not APFS. APFS is optimized for SSDs and can cause significant performance problems on an HDD. Also, Mac OS Extended (Journaled) is supported on all versions of OS X/macOS whereas APFS is not.


Step 2: move HDD to another old iMac High Sierra, HDD does not mount

No surprise there. I wouldn't expect a disk formatted APFS under Monterey to be usable on High Sierra. APFS underwent significant evolution after its initial release on High Sierra. (IMHO it was barely functional on High Sierra.) There were major changes in Catalina and later in Big Sur and further in Monterey. It may even be that the well known problems APFS had with HDDs back in the High Sierra era are related to yours not mounting on the High Sierra Mac.


Step 3: re-connect on iMac that was used to format the disc, which does not mount anymore. Disk utilisty cannot erase or re-format it. Error.

Somewhat conjectural, but it's possible that by connecting that APFS HDD to the old Mac running High Sierra, and High Sierra not recognizing it, that something got set/changed on the disk that couldn't be recognized by Monterey.


Step 4: connect HDD on a Mac Book Pro running 10.15.7. Bingo HDD mounts and all volumes are visible.

Also conjectural, but perhaps what may have been set/changed earlier on the HDD was ignored by Catalina (10.15.7).


As has already been suggested, this HDD should be reformatted as GUID Partition Scheme/ Mac OS Extended (Journaled).


Of course, the problem may have been, or also been, a hardware problem and/or a cable or connector problem. Others have already addressed those possibilities.




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User profile for user: MartinR
MartinR
User level: Level 7
24,053 points

Sep 30, 2025 7:13 AM in response to Oursamiel

Oursamiel wrote:
Step 1: on a iMac 27'', running 12.7.6 I format a brand new HDD using the AFSP scheme.
All volumes that are created are visible on the finder.

Not advisable. A spinning HDD should be formatted as Mac OS Extended (Journaled) not APFS. APFS is optimized for SSDs and can cause significant performance problems on an HDD. Also, Mac OS Extended (Journaled) is supported on all versions of OS X/macOS whereas APFS is not.


Step 2: move HDD to another old iMac High Sierra, HDD does not mount

No surprise there. I wouldn't expect a disk formatted APFS under Monterey to be usable on High Sierra. APFS underwent significant evolution after its initial release on High Sierra. (IMHO it was barely functional on High Sierra.) There were major changes in Catalina and later in Big Sur and further in Monterey. It may even be that the well known problems APFS had with HDDs back in the High Sierra era are related to yours not mounting on the High Sierra Mac.


Step 3: re-connect on iMac that was used to format the disc, which does not mount anymore. Disk utilisty cannot erase or re-format it. Error.

Somewhat conjectural, but it's possible that by connecting that APFS HDD to the old Mac running High Sierra, and High Sierra not recognizing it, that something got set/changed on the disk that couldn't be recognized by Monterey.


Step 4: connect HDD on a Mac Book Pro running 10.15.7. Bingo HDD mounts and all volumes are visible.

Also conjectural, but perhaps what may have been set/changed earlier on the HDD was ignored by Catalina (10.15.7).


As has already been suggested, this HDD should be reformatted as GUID Partition Scheme/ Mac OS Extended (Journaled).


Of course, the problem may have been, or also been, a hardware problem and/or a cable or connector problem. Others have already addressed those possibilities.




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User profile for user: Oursamiel
Oursamiel Author
User level: Level 1
4 points

Sep 29, 2025 11:38 AM in response to den.thed

Follow-Up


den.thed suggested to re-format the "reluctant" HDD differently, not APFS.


  • since one machine (MBP) accepts to mount this originally formatted HDD I used it to write another format, as suggested, Mac OS Extended (Journaled). Result using the MBP that accepts the disk is OK.
  • un-mount from MBP and try to re-mount on the iMac 27'': fails .
  • edit: precision: DiskUtility of the iMac 27'', reluctant to mount the newly formatted HDD says: uninitialized disk ... and after a while even this input disappears from the GUI of DiskUtility
  • as said above, external power and same USB cable for the HDD
  • tested USB port of iMac with another device indicates port is apparently working
  • stuck in the water ...
  • I may have to start to question the behavior of the actual "HDD to computer" interface, provided by an IcyBox in operation for about 10 years ...
  • second edit: after a few power ON/OFF iterations of the IcyBox, the "reluctant" HDD does show up in the finder as well as in the GUI of DiskUtility. Partitions are as defined.
  • The "smoking gun" could likely be the "IcyBox" HDD to USB interface ...
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User profile for user: HWTech
HWTech
User level: Level 9
68,192 points

Sep 30, 2025 11:38 AM in response to Oursamiel

First, make sure you erased the whole physical external drive instead of just the volume. This is especially important with new drives since the manufacturer may have used non-standard partitioning or included items hidden in an unused area of the drive which can sometimes interfere with different operating systems. Unfortunately Disk Utility hides the physical drives from view these days so you need to use the instructions in the following Apple article to reveal the physical drives:

Erase and reformat a storage device in Disk Utility on Mac - Apple Support


Second, if you will be using the APFS file system with older versions of macOS, you need to be careful not to use old versions of First Aid to repair the volumes since the newer versions of Disk Utility may be using a slightly modified APFS file system with extra or new features. Unfortunately macOS will automatically scan each volume when mounting it. It is possible the High Sierra file system check modified something incorrectly which renders the file system unstable. You could try erasing the whole physical drive as APFS on your High Sierra system which should eliminate this as a possibility.


Third, try using another USB cable from a respected brand making sure it is a high end cable. Too many cables these days are just enough to get by and are generally junk.....even the cables supplied by the manufacturer.


Fourth, some drives may need a bit more power, or perhaps a bit more stable power. Every computer is a bit different. Try connecting the drive to a powered USB3 hub to see if that makes any difference. I've seen numerous posts on this forum where some M-series Macs have issues with external USB drives unless they are connected to a hub (or perhaps a dock). If you are using a hub/dock, then try connecting the drive directly to the computer.


Fifth, maybe the drive you purchased is not a good one or may actually have a hardware issue. The quality of things these days is not always that great. Plus there are a lot of fake & counterfeit drives being sold out there as well as old worn out drives being sold as new (the drives' firmware has been hacked by the scammers to make the drive appear to be new....someone actually had to develop an app to see past this to confirm the true information stored elsewhere on the drive since this is becoming more common).


Six, perhaps you have some third party software installed which is interfering with the normal operation of macOS & is affecting the ability to access the external drive.

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User profile for user: den.thed
den.thed
User level: Level 10
90,376 points

Sep 29, 2025 8:08 AM in response to Oursamiel

I had the same problem with an APFS formatted HDD that I wanted to use with several Mac's on different macOS versions.


What fixed the problem, was to reformat the HDD Mac OS Extended (Journaled) instead of APFS.


Currently all of my external SSDs are formatted "GUID Partition Map/APFS" and work fine.

My remaining external HDDs are formatted "GUID Partition Map/Mac OS Extended (Journaled)" and work fine.

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User profile for user: Oursamiel
Oursamiel Author
User level: Level 1
4 points

Sep 29, 2025 10:31 AM in response to Oursamiel

Follow-Up


den.thed suggested to re-format the "reluctant" HDD differently, not APFS.


  • since one machine (MBP) accepted to mount this originally formatted HDD I ran another format, as suggested, Mac OS Extended (Journaled). Result using the MBP that accepts the disk is OK.
  • un-mount from MBP and try to re-mount on the iMac 27'' does not work.
  • as said above, external power and same USB cable for the HDD
  • tested USB port of iMac with another device indicates port is apparently working
  • stuck in the water ...
  • I may have to start to question the behavior of "HDD to computer" interface, provided by an IcyBox in operation for about 10 years ...


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User profile for user: Oursamiel
Oursamiel Author
User level: Level 1
4 points

Sep 30, 2025 12:16 PM in response to HWTech

Howdy HWTech,


thank you for your detailed suggestions. I will briefly answer along your list.


First: I agree and I was aware of that possible issue. The second attempt to re-format was done with DiskUtility that came with 10.15.7 and the physical drives were visible.


Second: As a matter of fact I don't "need" to be using the APFS scheme. As pointed out by Others, it was not optimized to be used with HDD, but rather with SSD. I'll stick to GUID Partition Scheme/ Mac OS Extended (Journaled).


Third: yes, I'm also aware of that. I use this only cable for my HDD rotation scheme and thus far it has been OK. Swapping cable did not improve the situation.


Fourth: the power source (PS) used for my HDD ** rotation scheme delivers 4A DC and was, thus far, never a problem. I have tried another PS, no improvement. Indeed, I'm connecting this "reluctant" HDD as well as all others to a SATA / USB interface, with its own PS.


Fifth: possible indeed. I tend not to buy that immediately since I bought several of these drives together for a NAS and this one is the last one. 1 year old, never used, respected brand, designed / sold for NAS use.


Six: possible indeed. What is striking is that other drives are not affected.


As of writing, I'm seriously questioning the reliability of my SATA / USB interface, provided by a dock. I need to borrow a piece that does the same to be able to compare.


Again thank you for the time to provide FB. Regards, Philippe



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User profile for user: Oursamiel
Oursamiel Author
User level: Level 1
4 points

Sep 30, 2025 7:45 AM in response to MartinR

MartinR, thank you for your detailed answer.


I overlooked the issue with AFSP because the High Sierra machine has an internal disk formatted this way. After checking it turns out to be an SSD ... The other internal disk of the High Sierra machine is indeed a mechanical (spinning) HDD and formatted as you and others have suggested GUID Partition Scheme/ Mac OS Extended (Journaled).


Beyond this, Step 3 remains a "mystery" as well as Step 4 which luckily turns out to be my only chance to modify the formatting scheme without asking for external help.


The "reluctant" HDD is now reformatted using the GUID Partition Scheme/ Mac OS Extended (Journaled) scheme.

Interestingly, this device does not mount on the High Sierra, nor on the Monterey machine without fuss. On occasion it mounts on others not. No fuss at all on the MBP running Catalina.


By elimination I'm must question the quality / reliability of the SATA / USB interface, provided by a docking station that I have been using flawlessly for many years with a series of ** discs. Other discs do not seem to be concerned however ...


Again, thank you for your time in providing useful input. Regards, Philippe






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User profile for user: Oursamiel
Oursamiel Author
User level: Level 1
4 points

Sep 29, 2025 8:18 AM in response to den.thed

den.thed, thank you very much for the suggestion to re-format the "faulty" disk not using APFS.


I can try that, since one (of three) machine recognizes the disk.


There is a little "however": how do we explain that the machine that performed the first formatting of that HDD is reluctant re-mount the device afterwards. On that particular machine, its internal disk uses APFS.


I'll try and report.

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HDD not recongized by mac that was used to format it

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