External Harddrive EFI partition will not mount

You can use First Aid to repair the out-dented disk entry by selecting it for the repair. Then repeat for the indented entry.

An exit code of 8 means the routine failed. Frankly, here's what I would do when all else has failed. At this point, I assume the drive may need to be re-partitioned. I do this:

Drive Partition and Format in El Capitan and Sierra

1. Restart the computer.
2. Immediately after the chime press and hold down the "COMMAND" and the "R" keys together.
3. Release the keys when the Utilities Menu appears.
4. Select Disk Utility then click on the Continue button.
5. After Disk Utility loads select the drive (out-dented entry with the mfgr.'s ID and size) from the side list.
6. Click on the Erase tab in Disk Utility's main window. A panel will drop down.
7. Set the partition scheme to GUID.
8. Set the Format type to Mac OS Extended (Journaled.)
9. Click on the Apply button, then click on the Done button when it activates.
10. Quit Disk Utility and return to the Utility Menu.
11. Select Reinstall OS X and click on the Continue button.

This will erase everything on the drive but should put it back to normal. If it does not then you have a bad drive.

See below:

/dev/disk2 (external, physical):

#: TYPE NAME SIZE IDENTIFIER

0: GUID_partition_scheme *1.0 TB disk2

1: EFI EFI 209.7 MB disk2s1

2: Apple_HFS TOSHIBA EXT 999.9 GB disk2s2

The actual physical drive is disk2, but the logical volume is disk2s2 and called TOSHIBA EXT and is formatted as an Apple_HFS. If you want to try mounting it you would use: diskutil mount /dev/disk2s2 or try diskutil mountDisk /dev/disk2. See if one of those work. If they don't then open Disk Utility in your Utilities' folder. You should find the listing for the external drive that is out-dented. Indented below it is the actual logical volume. It will appear grayed out if not mounted. I would reformat the disk unless you have data to rescue.

Did you try: diskutil mountDisk? You might try:

diskutil unmountDisk force disk2

or

diskutil unmount force /dev/disk2s2

If one or the other does work, then disconnect the drive, wait 10 seconds, then reconnect it. See if you can open Disk Utility.

Well, I'm puzzled. Usually, one of all the above works with a fussy drive provided the drive isn't bad. Yours seems to be partitioned and formatted properly, so I don't really know what's going on given that I'm working blind. I think I would shut down the computer, turn off the drive if it's powered, then disconnect it. Then I would reconnect the drive and reboot the computer from the Recovery HD. Open Disk Utility from the Utility Menu and see if that drive appears in Disk Utility. If it does I would use First Aid on the out-dented drive entry and then on the indented volume entry. If you still get nowhere, then sent it back to Toshiba and exchange it under the warranty.

Where is Parallels keeping its disk? Did you check how much space is on it? The error was produced by Parallels. I don't know in what way this is relevant. Or is this on the external drive? If all these problems are related to Parallels pseudo-disk that is stored on the external drive, then these problems have nothing to do with the hard drive itself.

I think the drive has become corrupted or it has failed or is failing. Assuming the problem is the former, for now, I think you have only two directions to go. The first is to erase the drive and repartition and reformat from scratch. This means you need to be able to backup your data stored on the drive unless you can afford to lose it. You would need a backup drive large enough to hold all the data currently stored on this drive while you go through the procedure. The second is to get the utility, Disk Warrior, and use it to try and restore the drive to working status. DW will cost $99.00. There is no guarantee it will work, but it has saved my bacon more times than I care to remember.

If the drive is failing then you will need to replace it. Unfortunately, there remains the problem of trying to transfer the files to a new drive. If you take the Toshiba with you to a local Apple AASP certified service provider or to a local Apple retailer, they may be able to fix the problem or transfer the files to a new drive.

I'm afraid I don't have better news or a solution that will work. How old is the drive? If it came with a three-year warranty and is under warranty, then Toshiba should be willing to replace it at no cost to you.

I don't think it would matter, but I am only moderately familiar with Unix. I rely a lot on a third-party utility called Dash. It is an easier to use Man reader that isn't free. I don't mind experimenting on my computer, but I wouldn't wish to do that on someone else's computer. I'm not sure how effective 'cp' would be.

I did come across this:

A. Fix Permissions for a Locked Drive

Open Terminal in the Utilities' folder. Paste the following commands at the prompt. Press RETURN after each. The first command will prompt for you to enter your admin password. It will not be echoed to the screen. After entering your password press RETURN again.

sudo chflags 0 /Volumes/*

sudo chmod a+rx /Volumes/*

killall Finder

How do you know the 1TB drive is unmounted? If it is, then leave it connected and restart the computer to see if it now is on the Desktop.