Cant format SSD using Disk Utility

When you follow the instructions & link provided by @PRP_53 to erase the external drive, does Disk Utility see the physical drives? By default Disk Utility does not show the physical drives unless you follow the instructions provided by @PRP_53.

Make sure you allow macOS to connect the external drive if you are using an M-series laptop. macOS should pop-up a prompt asking if you want to connect the external drive, but sometimes this pop-up gets hidden or does not show. I personally prefer to configure the Privacy & Security System Settings to "Allow accessories to connect" as "Always when unlocked" which gets around that issue & the annoying inconvenience of pop-ups.

If your Mac asks you to allow an accessory to connect - Apple Support

If macOS does not see the physical drives, then you have a hardware issue of some sort. It could be the cable, the drive, or the port. I have seen some people on this forum report that some drives seem to need to be connected to a USB3 hub instead of directly to the computer.

If you see the physical drive, but are unable to erase it by following the Apple instructions @PRP_53 provided, then I can provide instructions for using the command line to write zeroes to the beginning of the drive to destroy the existing partition table. macOS for some reason can get confused if something unexpected is encountered.

rgma62 wrote:

I recently bought an external SSD to use for Time Machine. I formatted it for Mac (APFS) and then set up Time Machine to back up. It failed repeatedly. I thought the disk may be faulty so bought a second SSD from another company and exactly the same thing happened.

Now neither drive will mount and Disk Utility can First-Aid or erase either drive.

Im using a MacBook Air M3 from 2024 running Sequoia 15.3.2.

What's going on? I read somewhere that Sequoia doesn't like SSDs and Time Machine but couldn't find it again, is this right?

Not True at all

If and only if you installed some Third Party Software that came Bundled with these SSD Drives

Remove it as per the Instructions from the Makers of these Drives

Erase and reformat a storage device in Disk Utility on Mac

rgma62 wrote:

I formatted it for Mac (APFS) and then set up Time Machine to back up. It failed repeatedly.

How did it fail? What are the exact error messages? Screenshot is best.

Please post your 'instructions for using the command line to write zeroes to the beginning of the drive to destroy the existing partition table.'

Before this, if the drive was designated as a TM backup drive, then go into the TM app and tell it to forget/stop using the drive as TM to see if you can erase it normally using Disk Utility using the link provided by @PRP_53 (read the instructions so you are erasing the whole physical drive and not just a volume):

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

To use the command line to destroy the partition table on the drive, you will first need the device identifier for the physical drive. It is best to disconnect all other external drives (or anything that appears like a drive with a device identifier) so that you don't accidentally destroy data on the wrong device since there are no safety nets when using the command line. The device identifier may change every time a device is reconnected or the system is rebooted so it is important to get the current device identifier for the physical drive you want to erase right before using the command line. In the picture of Disk Utility provided by @PRP_53, you can see the physical drive "WD Elements 10B8 Media...." has a device identifier of "disk4".

Here are the commands needed to unmount all volumes on the specified device. In my commands you need to replace "diskX" with the correct device identifier (using the example already mentioned you would replace "diskX" with "disk4".

diskutil  unmountDisk  diskX

sudo  dd  if=/dev/zero  of=/dev/diskX  bs=100m  count=10

The second command is the dangerous one if you provide the wrong device identifier for "diskX" as it will destroy the data on that device. It will prompt you for your admin password. Nothing will appear on the screen as you type the password, so press the "Return" key to submit the password.

If there are no errors, then use Disk Utility to erase the physical drive using the instructions in the linked Apple article.

rgma62 wrote:

Thank you for your reply. No partitions were created. I reformatted the drives from Windows to APFS and ran Time Machine.

I think you maybe confused

Microsoft Windows formatted to Apple's Propitiatory APFS format ?

Time Machine Backup is Only found on Apple Computers running macOS from Apple - Full Stop

If you Formatted the Drive is Microsoft Windows

The Drive could in in MS Windows format NTFS

Even a NTFS Formatted Drive should mount in Apple macOS Disk Utilities

Thereby allowing you to Reformat the drive to APFS / GUID Partition Map

My apologizes but this " I reformatted the drives from Windows to APFS and ran Time Machine. " may have confused me

Neither drives can be mounted or reformatted on" MacBook Air M3 from 2024 running Sequoia 15.3.2. " ?

If you have a Windoze machine reformat the drives to say exFat

Move the drive (s ) back to MBA

Can you Mount the drives in Disk Utilities ?

Can you Erase the Drives ?

rgma62 wrote:

Please post your 'instructions for using the command line to write zeroes to the beginning of the drive to destroy the existing partition table.'

I have sometimes formatted a drive first as FAT (MBR) and then to the desired APFS (GUID), for example. I guess that resets the partition table the same way as via the Terminal?

I have 2 HP P500 SSD drives USB-A, 1 WD 500GB SSD USB-A and 1 Segate 500GB USB-A SSD drive

Each where Out of the Box formatted in a Windows format

Using a cheap USB-A to USB-C passthrough toggle

Connect any of the above mentioned drive drives a M3 MBA, that started with macOS 14 Sonoma and since upgraded to macOS 15.4 Sequoia

Using Disk Utilities - each drive will Mount and can Reformat each drive directly from the MS Windows format to APFS / GUID

In the 20+ years in the Apple Eco-System , have never experiences such behaviours with External Drives

What you are describing seems Unique and Localized to your setup

I should disclose

The same External Drives previously mentioned, have also moved from the M3 MBA to a M4 Desktop and to a M2 Mac Mini

Each running the same Sequoia 15.4

Any and all the drives can be and have been reformatted several times without issues

I don't know whether this will help. but at some point I was trying to erase and format an external drive on Disk Utility and it wouldn't work.

I rebooted the Mac using Disk Recovery, and was able to format using Disk Utility in Recovery.

Besides APFS are you sure you used GUID partition? Should have no issues using an SSD.