Can't partition (option greyed out) External HDD on Mac OS X El Capitan

Issue the following Terminal's command

diskutil erasedisk hfs+ External GPT /dev/disk2

I solved this issue by using Disk Utility by going up to the Menu bar, selecting "View", and selecting "Show All Devices". Then, the erase and partition buttons became active. I didn't have to get into Terminal at all.

I have almost the same problem. My external HDD already has data and partition. First, the new Disk Utility interface threw me off. This is the new interface?

The HDD had 2 data partitions (160GB each), both of which I managed to erase. The third part is titled "BUFFALO Virtual CDrom Media" and has 0.8GB Uninitialised. It is an old HDD and I can't remember why it was set up like that. In all three (the two partitions as well as the Uninitialised portion), the partition is greyed out.

The other HDD I had, had two separate partitions, Backup 1 & 2, 1TB each. I erased Backup 1 but again the partition was greyed out and I am not able to further partition it or partition the entire HDD.

I tried the suggested Terminal command and got this:

Last login: Tue Jan 31 12:28:11 on ttys000

RobertscBookPro:~ robertxxx$ diskutil erasedisk hfs+ External GPT /dev/disk2

Started erase on disk2

Unmounting disk

Creating the partition map

Waiting for partitions to activate

Formatting disk2s2 as Mac OS Extended with name External

Initialized /dev/rdisk2s2 as a 465 GB case-insensitive HFS Plus volume

Mounting disk

Finished erase on disk2

RobertscBookPro:~ robertxxx$

To no avail, I still have the PARTITION icon dimmed.

This is the info of the external Samsung SSD T3

Volume name : External

Volume type : Physical Volume

BSD device node : disk2s2

Mount point : /Volumes/External

File system : Mac OS Extended

Connection : USB

Device tree path : IODeviceTree:/PCI0@0/XHC1@14

Writable : Yes

Is case-sensitive : No

File system UUID : 1B65CCC5-5FD0-34D9-AC1C-90C51234C0B0

Volume capacity : 499,763,888,128

Available space (Purgeable + Free) : 499,357,732,864

Purgeable space : 0

Free space : 499,357,732,864

Used space : 406,155,264

File count : 53

Owners enabled : Yes

Is encrypted : No

System Integrity Protection supported : No

Can be verified : Yes

Can be repaired : Yes

Bootable : No

Journaled : No

Disk number : 2

Partition number : 2

Media name :

Media type : Generic

Ejectable : Yes

Solid state : No

Parent disks : disk2

What can I do to partition the SSD?

Robert

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HELP PLEASE!!!

i didn't know if I executed this command diskutil erasedisk hfs+ External GPT /dev/disk2

my hd would be erased... i lost everything, please help.... is there anything i can do to get my files back??

From hrhee0

This command deletes all of your data on your external hard drive if there's still content on it. So what I did was I used this, then I downloaded Stellar Phoenix Mac Data Recovery - instant download link <http://download.stellarinfo.com/StellarPhoenixMacDataRecovery.dmg.zip>. Run a scan and recover all the data that was on it

It works.

Leo

Same problem for me.

However, I have kept a version of Mountain Lion on another partition (internal). I booted into this partition, ran disk utility and had no problems in partitioning the external USB3.0 disk - actually a naked WD 750Gb 2.5" disk in a dock, into two partitions.

Why is it that OSX 10.8 can do trouble free, what 10.12 cannot? Surely this is a problem for Apple? Please fix this.

Tom Boone wrote:

From looking over than command it looks like this will "erase disk." Is that correct? I'm looking to keep all of the data without having to format the disk.

Yes, that's correct. The command will completely wipe your disk.

The original poster of this thread couldn't partition his external hard drive via Disk Utility. Plus there was anything at all on that disk. So I suggested to reinitialise that particular disk using Terminal.

If you are looking to RESIZE the actual partition on your disk use Disk Utility.

Use Terminal only if you are skilled enough on the command line. The resizeVolume is the correct verb to use in that case. See the below syntax

diskutil resizeVolume
Usage:  diskutil resizeVolume MountPoint|DiskIdentifier|DeviceNode size
        [part1Format part1Name part1Size part2Format part2Name part2Size
        part3Format part3Name part3Size ...]

Non-destructively resize a disk.  You may increase or decrease its size.

When decreasing size, you may optionally specify new partitions to create
to fill the newly-freed space.  Specify these new partitions as in the
diskutil partitionDisk command.  A size of zero will cause a grow fit-to-fill.
Ownership of the affected disk is required.

Valid sizes are floating-point numbers with a suffix of B(ytes), S(512-byte-
blocks), K(ilobytes), M(egabytes), G(igabytes), T(erabytes), P(etabytes),
or (%)percentage of the total size of the whole disk.

A size of "limits" will print the valid range for the current conditions of
the file system and room to grow up to an immovable object (next partition).

A size of "R" for the target partition will resize it to the maximum
possible; "R" cannot be used for the size of new partition triples, if any.

resizeVolume is only supported on a Journaled HFS+ file system.

Experiment on a disk that has no data at all on it.

If you need further assistance, please start your own thread. This one is marked as solved.

And, be sure to have a recent backup before playing around with partition 😉

oh thank you so much, had to tell it,

such a drag from apple, unbelievable, getting always worse!!

thank s again, after days only this worked, or reformatting on a PC

(one day I want to know how did you know)

thank s again

I solved this issue by using Disk Utility by going up to the Menu bar, selecting "View", and selecting "Show All Devices". Then, the erase and partition buttons became active. I didn't have to get into Terminal at all.

PQ:

NP. I did too, at first.

Go back a page and find eunicekhong's post. it has an image of the Disk Utility window we're talking about. Look at the left column, at the very first entry, at the top of the column. It looks something like: APPLE SSD SM0256G Media. (that is my HD, not the one by eunice, but I didn't want to go back a page and lose this msg.)

see it?

Hi, Alberto!

I stupidly pasted the 'diskutil erasedisk' command into Terminal without checking my disk device labels 😕

The erase process started immediately and began erasing the disk I did not mean it to.

I cancelled/terminated the process within 10 seconds.

The disk is now showing as empty in Disk Utility. It also won't eject properly. A TimeMachine backup was being made at the same time I used the command.

How quick does the 'diskutil erasedisk' command work and do you think there's any chance that the disk has not been (entirely) erased?

Thank you 🙂

This identical terminal command worked with my Lacie 1TB drive that showed up as 272.6 GB after using Disk Utility and Erase... (formatting either at MAC OS or MS-DOS [FAT]).

After running the terminal command the drive shows up as 999.86 GB, and now the partition button is active in Disk Utility. Thanks, much!