If you always connect your external hard drive to Mac to run Time Machine backupa, there are times where you will notice that the external hard drive doesn’t show up in your Mac. If you are facing this issue, here are some fixes for you.
Most problems with drives on a Mac are caused by a poor connection, so the first step to troubleshooting the problem is to ensure your drive is actually connected to your Mac properly. If there’s a light on the drive, is it turning on? If it’s a spinning disk, do you feel the drive spinning through the hard drive’s case? Try a different port and different cable to confirm that these are not issues. If possible, use good, known hardware, like a USB cable that you recently used to successfully connect a device previously.
Check Disk Utility
Disk Utility will list drives both mounted and unmounted. It’s possible for a drive to be connected to your Mac and for the operating system to notice the drive but not mount it. Mounting is the last step between you and your data. However, a failure to mount is sometimes for a good reason. The disk formatting might be corrupt or unsupported by the Mac, preventing it from mounting properly. But sometimes all it takes is a quick tap of the Mount option to get things working.
1. Open Disk Utility, found in “/Applications/Utilities”
2. Look at the drawer on the left of the application for a description of your drive. The descriptions can be cryptic, but normally manufacturer name and size will help you locate your target drive.
3. Right-click on the greyed-out volume you want to mount in the drawer on the left and choose the “Mount” option in the context menu.
Use Terminal’s diskutil Command
diskutil Terminal command, you can get slightly more insight into your disk mounting than Disk Utility may provide, sometimes showing drives that are hidden from Disk Utility for various reasons.
1. Open Terminal from “/Application/Utilities.”
2. Type the command below and press Enter:
3. This will show a list of all the drives currently visible to your device, mounted or otherwise.
4. If you see the disk in the list, but it’s not visible in Finder, you’ll want to try mounting it with Terminal. Run the command below using the correct device name (disk2, disk3, etc). It will automatically mount all mountable and UI-browsable volumes on the given disk when run.
To mount a specific partition, use the mount command with the correct disk identifier, visible in the right-most column of diskutil list’s results.
If the partition is mountable and readable, it will be mounted. If the format is not fully compatible with macOS, like NTFS, then the drives may be mounted as read-only.
Formatting describes how the data is organized on the disk. Your Mac needs to support the hard drive’s formatting. If your Mac cannot understand the formatting of the drives, it may attempt to initialize them. This will erase the disk and reformat it as a format that macOS can read. Do not press this button unless you want to erase the disk.
There are a couple of places you can find the formatting of a disk:
In Disk Utility, it can be found underneath the drive’s name with the disk selected in the left pane.
In Terminal, run
diskutil info disk3, using the disk number from diskutil list.
If the format is not readable by macOS, the system might describe is as “uninitialized.” This just means the Mac can’t understand the system, not that the drive is blank. Once you know the formatting, you can find a way to mount a drive with that formatting on your Mac.
If your drive doesn’t mount on macOS, it’s probably not connected properly. Try a second port before digging into troubleshooting steps like those above.