Option, Command, P, and R. It should look as though your Mac has started again; if it has, release the keys when you hear the second startup chime. Hopefully, the hard drive has shown up now. Disk Utility is within System Preferences, or you can find it using Spotlight.
External Hard Drive Not Showing Up on Mac – What to do
If it is visible, then click the option to Mount, which should make it visible on the desktop and in the External Drives option in the Finder menu. But there might still be a way you can recover the data on the external drive.
In the Sidebar tab you can choose which folders and devices will be shown in the left-hand column of the Finder window. If your drive is having problems, you can try to fix them yourself with First Aid and therefore get access to your files. First Aid tool will check the disk for errors and then attempt a repair as needed.
Before We Begin: Read-Only Volumes and NTFS
It helps to verify and repair a range of issues related to startup HD and external drive problems. If you are able to fix the hard drive or SSD in your Mac or a external drive using Disk Utility you will hopefully be able to recover your files.
If First Aid successful in fixing errors, the external drive should be available to mount. If the utility unable to repair issues, your drive truly broken or formatted using a file system that the Mac cannot read - in this way we suggest you follow the next steps to recover data from a damaged disk drive.
Thankfully, there is an app for that. This is a sub-folder within the Applications folder, with a crossed screwdriver and wrench on the folder icon, while Disk Utility looks like a hard drive being examined with a stethoscope.
Lacie external hard drive not showing on … - Apple Community
Both of them will be referenced a lot. First we will check the basics, and from there we make sure that MacOS is set up to display external drives, can mount the drive, and that the drive has no errors on either the disk itself or its file structure.
As William Ockham once said, the simplest solution tends to be the best one. Considering that, let us check all the basics first. Get into the habit of doing this with any computer issues, as it can save time, money, and hassle in the long run.
This happened to me many years ago. At that time I found to my surprise that a disk is detected or not by its stamp, found in the first few bytes in the first sector. If one of these bytes is corrupted, the disk is lost. This is called the Disk Signature.
Lacie External Hard Drive Stopped showing up on my Mac
At that time, I solved the problem by copying these bytes from a similar disk, but I really don't remember how many bytes I copied or using which tool. TestDisk might do the job, as explained in the article How To Fix: It seems the partition map of your external hard drive is damaged badly and Disk Utility doesn't repair the map though you can erase your ext-HDD afresh and map a new partition map on it.
It's good you already have the backup and data recovery isn't your priority here. Usually, people ask for the data recovery from such a drive. I am interested to know how data recovery application didn't help you?
Some tools can recover data from a troubled or unmounted volume.