Q: Disk Utility won't mount a disk

Launch/Utilities/Terminal and enter this command at the prompt:

diskutil list

Press return.

If it sees the disk, note the number of the disk (far left column) you want to mount.

Then, enter this command:

mount /dev/(number of disk)

Put in the number no parenthesis.

Press Return.

Also might try

mount force /dev/(number of disk)

I would start with the basics. First, what is the external enclosure, firewire or USB? Did you check if there is a firmware update for the enclosure itself? I had this problem with a My Book II enclosure from Western Digital and updated the firmware then the disk finally mounted. If that is not a problem, do you have another hard drive you can try in the enclosure to rule it out as the culprit? or another enclosure or computer to try it out on?

Then once you know with 100% certainty that the external enclosue is fine, you can try Disk Warrior which does sometimes mount disks that DU won't see. Tech Tool Pro and Data Rescue are also sometime good with these issues.

Hi Tod, I'm trying your advise but please correct if I'm doing wrong Macbook pro with upgraded Yosemite): I connect my WD passport studio with firewire (that does not mount or show in Disk Utilities), and use your CLI command but what do you mean with (number if disk)? I tried all the numbers on mine but does not work. It keep on saying: You must specify a filesystem type with -t.

Please help?

Cheers

Marius

Sorry I dont understand what you mean with "number of disk"? What number?

Marius

Ok figured it out, and got the message: mount/force/dev/disk2: No such file or directory

What now?

I also tried TechTool pro 7, still don't mount. It gets power but don't mount.

Marius

Very similar problem.  Bought a used mid 2010 Macbook Pro 13 inch that would not recognize internal HD.  I swapped the internal cable from my working 2009 MBP 13 inch and, BINGO, everything works!  Too bad the cable is $50 since it also carries the IR sensor signal and lamp. 

Its odd that such a cable would "fail" - maybe its the circuit board connector?

Well - may not be "cable" after all. I switched the "bad" cable to the computer that originally had the "good" cable - booted right up.  Meanwhile the "good" cable when placed in the computer that wouldn't boot also works!  Could be the connector or maybe a crack in the ribbon conductor that works when the cable is bent a certain way.

I am unamble to mount the external disk, tried force mount

i have the following msg

what do mean by filesystem the with -t

pls advice

rahul

Hi, I have exactly same problem, my hard drive Transcend 2TB is working perfectly on windows.  On mac, i have a Macbook Pro and a Macbook 12 in brand new.  First time i connect it worked fine, but now its random.  Sometimes i can take up to have an hour of rebooting to get my HDD running.  It powers up but not recognised.  Both Macbook pro and Macbook same behaviour.    Read something about reseting the PRAM, using the keys: COMMAND+OPT+P+R at the same time when rebooting it also works randomly.  Very frustrating.  Looked for the drivers update of the HDD no luck.  Used the DISKUTIL DISK command on the terminal.  It does not list it. Not working.  Also, called Apple support, they mentioned that it was the HDD Format, so suggested MAC OS X Extended format.   So took a day work.  Worked the first time connected , now random.  Frustrating.

Please, useful advices???

You might want to consider starting a new discussion. Since this one is marked solved, less people are likely to look at it. You can link to this one.

This is what I got.  But drive still not mounted.