Can't encrypt external hard disk using High Sierra

I had the same problem (no encryption options, partition button greyed out) and also solved it. In my case, the problem was that my new drive (La Cie Rugged Thunderbolt from the Apple Store) came with a master boot record partition map and not GUID. If a drive is not GUID, neither the partition button nor the encryption settings are available in the graphical Disk Utility, which is why we're forced to use the command-line diskutil to partition first.

In the Terminal app, I used:

diskutil list

to find out that my new drive was mapped to /dev/disk2. Then I used the following:

diskutil partitionDisk /dev/disk2 GPT JHFS+ YourPartitionName 0b

...to partition the disk using a GUID partition map (GPT is the argument that specifies GUID) and Journaled HFS+.

This ran successfully and the encryption and partition options became available in Disk Utility.

This post has a good overview of how the command's arguments work so you can be sure of what you're getting:

http://www.theinstructional.com/guides/disk-management-from-the-command-line-par t-2

Hope this helps others not waste as much time as I did trying to make this work.

Non-Terminal Solution: (to make the drive GUID)

1. Disk Utility > "View" (Top Left Corner) > "Show all Devices"

You will now see the full drive (not just the partition) on the left side.

2. Right click the drive in question (top drive, not the sub partition) > "Erase ..." :

"Name: Untitled"

"Scheme: GUID Partition Map"

"Format: .... Encrypted options will now be available.

3. You will be prompted to enter a password.

You don't have to use terminal at all to change the partition scheme. You only have to change the sidebar view in DiskUtility in order to select the device instead of the volume, from there on you can choose the partition scheme on erasing the drive like in previous versions of DiskUtility.

For whatever reason, you must first erase it as GUID and MacOS Extended (Journaled).

Then, erase it again with the encryption option turned on.

Or, Right-click on the disk in Finder and choose to Encrypt it.

It doesn't seem to allow going from a different partition scheme straight to encrypted.

Just to be clear, and to give foolproof instructions, is this what should be entered in Terminal? (The name of the external hard drive I am trying to do this with is named “Silver HDD”):

diskutil partitionDisk /dev/silver hdd 1 GPT HFS+ newdisk R

After using the above, do I then need to enter this into Terminal?

diskutil eraseDisk HFS+ newdisk /dev/silver hdd

Anything else?

Per: terminal - How do I force a partition and format on a USB key in OS X Mountain Lion Disk Utility or from CLI diskutil? -…

Ok, that didn’t work. Here is what did and finally got Disk Utility to give me the encryption option using this command in Terminal first:

“diskutil list” to get a list of the mounted disks (I only had my one internal drive, which is in just one partition). Thus, the external drive I wanted to reformat/erase was the third in the list and indicated by “disk 2”.

Then, I used this command where I “Silver” was the name I wanted to name the new formatted disk:

“diskutil eraseDisk JHFS+ Silver disk2"

After doing all that, I then used the regular Disk Utility application to “Erase” the disk and selected the encrypted option.

Hope this helps!

(I found part of my solution from this site: https://www.maketecheasier.com/format-external-drive-osx/)

Very helpful trick and very easy to do: 2 minutes and that's it!

Thanks a lot Pierre!

I was suspecting that the problem was coming from this LaCie disk that I bought in the Apple store.

Strange that they are not including this GUID partition...

Read Protect a disk with a password using Disk Utility - Apple Support.

At the least, you'll need to escape the space in your hard drive name:

diskutil partitionDisk /dev/silver\ hdd 1 GPT HFS+ newdisk R

diskutil eraseDisk HFS+ newdisk /dev/silver\ hdd

Thank you so much. This was doing the trick. Finally managed to tame my external drive.

Thanks again!

Thanks, seems to have worked for me.

Best answer...worked