My new external Mac drive is read-only. How can I fix it?

This is so weird: I just bought a new 500GB external hard drive but when I hook it up to my iMac, I get a little "not allowed" symbol every time I try to copy anything onto the device! Digging around, it appears to be connected "read only". HELP!

Dave's Answer:

While the majority of the time you should be able to just plug in any sort of external hard disk or drive, sometimes Mac OS X does get a bit picky about write permissions based on how the drive is initially formatted. In particular, it doesn't natively support computer drives that are formatted as NTFS, the Windows NT File System, a very efficient file system designed for Windows computers that supports extremely large file sizes.

I had a similar experience myself when I hooked up my new 2TB external drive to my Mac Mini server, so I can show you how I fixed the problem. I will say that initially I too was befuddled and closely examined the hard drive itself to see if it had a "read only" switch. It didn't. :-)

So here's what I saw when I looked at the drive on the Mac, within the Finder:

Notice the lower left corner? I've highlighted it: the pencil icon with the line through it. That's the Mac's subtle way of saying that you can't write to it.

Chose File --> Get Info... to get more details:

Again, you can see on the bottom that it says I can only read the drive contents, not write to it. Dead useless as a backup device, for sure!

To fix it, the path I took was to let the Mac erase and reformat the drive, figuring that since it was empty, there'd be nothing lost and I would be confident that it was then completely compatible with my Mac systems.

The program you want to accomplish this is in the Applications folder, within Utilities: Disk Utility. Start it up and you'll see all the drives listed on the left side. Click on your new drive on the list to proceed:

mac disk utility external read only erase

You'll want to click on the "Erase" option along the top after you've picked the drive. In my case, it's "2 TB WD Ext HDD 1021..."

Now you can pick which format should be used when the disk is rebuilt from the list:

mac disk utility erase pick format extended

Since I know that I'll never plug this drive into a PC, I'll choose a Mac disk format, and of those, extended journaled is your best bet. If you wanted to have it be PC compatible, use MS-DOS format, but be warned that my experience is that read/write speed suffers on the Mac because of it having to reorganize data as it hits the drive.

Give the drive a name -- I chose "Insurance" for mine -- and click on "Erase..."

Ayup, there's nothing on the disk, so let's proceed. Click "Erase". The resultant action will take a few seconds up to a few minutes or longer, depending on your drive size and speed...

Once it's done you're also done and good to go. What you might see, however, is a prompt asking if you want to use the drive with Time Machine if you're running the slick Apple backup software:

I don't want to use it - I already have a disk drive specifically for Time Machine - so I click on "Don't Use".

Now, finally, one more peek at the newly renamed drive with "Get Info...":

That's solved the problem, and I am off on my merry backup journey. Hope that helps you out too!

If you're dying to have NTFS support, btw, it appears that the only solution i to install some third-party software, specifically either MacFUSE or NTFS-3g.

Categorized: Mac OS X Help (Article 9459, Written by Dave Taylor)
Tagged: disk reformatting, disk utility, mac disk formats, mac file systems, mac os x, NTFS, ntfs support
Previous: What are the cool third-party Mac OS X screen savers?
Next: How do I request a payment via Paypal?

Subscribe!

Never miss another Q&A article! Click to subscribe:

Comments

my lecturer forwarded powerpoint presentations to the class which are password protected. All students with windows are able to view them as a read only doc, however,those of us using Mac are not not able to view them at all. Is there some way I can i view password protected documents as read only on Mac??

Posted by: Charmaine at September 19, 2010 4:08 PM

Charmaine, not sure what to suggest, as I haven't encountered this situation before. Can one of your PC-toting classmates try doing a "File -> Save As..." and try to create a new copy of the slideshow that you can read? Or ask your prof to share it in PDF format so that it's more widely readable by the students?

Check this out too, though I'm not sure it'll be helpful: http://support.microsoft.com/kb/953823

Posted by: Dave Taylor at September 19, 2010 4:30 PM

Thank you! This was exactly what I needed to know, in a language I can understand!

Posted by: Matt at November 2, 2010 8:39 PM

After going through the steps in the reply to "My new external mac drive is read-only. How can I fix it?" on askDaveTaylore.I was able choose a new format and create a title for the drive, however, upon clicking erase and answering yes to erase the drive, and error occured stating, "file system formatter failed." What now??

Posted by: Natalie Smallwood at December 3, 2010 11:18 AM

Natalie, this sounds like a hardware problem. I'd do this: try a different cable, plug the drive in again and try to format it. If that fails, I fear you might have a bad drive or one that has a hardware problem that's causing it to be unformattable. You can buy new ones - including 2TB or larger - for about $75 so your best solution is probably to replace it if it's still failing. Good luck!

Posted by: Dave Taylor at December 3, 2010 11:35 AM

Thanks for this help. I bought a Seagate drive that said it needed to be reformatted for Mac and I could not find this info on Seagate's website.

Posted by: David Senft at December 23, 2010 11:03 AM

Thanks so much!

Posted by: Samuel Giorgievski at January 3, 2011 11:39 PM

my external HD has info on it I don't want to erase. I've used it before but since getting a new HD installed on my mac it is only read only. Is there a way to change it without erasing all the information on the HD?

Posted by: Daniel at January 10, 2011 10:48 PM

This was perfect! Thank you so much for the easy how to guide with pictures. I was really nervous that mine would not work until I found this website so thank you so much

Posted by: Andy at January 15, 2011 2:44 PM

I bought the exact same external HD as you did. So glad I found this!!!

Posted by: Faith at January 16, 2011 10:47 PM

It says cannot unmount disk or something.

Posted by: Dennis at January 21, 2011 2:49 PM

Hi Dave
Do you know if there is any way to get a mac to read an external drive Itunes library that was created on a PC. I've just moved to Mac and loving it only niggle is the Itunes library I followed all the consolidation steps etc in different forums but cant see the items in the library I believe possibly because of the file path reference used by windows in the library file, i can manually open a movie or music and it plays OK and then appears in Itunes as it should. I've got something like 600GB of a library so it would be a slow journey doing it all manually. Any advice appreciated.

Posted by: Trev at April 7, 2011 10:39 AM

Very very helpfull, thank you very much.

Posted by: Franz at May 12, 2011 8:05 AM

Hi, I used my WD 1TB hard drive with my iMac 24". I upgraded to iMac 27" and my hard drive is in "read only" mode as well. Is there a fix to make it workable without deleting all of the data?

Thank you!

Posted by: Val at May 19, 2011 11:25 AM

This worked! Thank you!

Posted by: Danielle at May 26, 2011 9:33 PM

Will doing this delete all the files on my hard drive?

Posted by: AGeraghty at June 22, 2011 2:35 AM

Thank you! I wish everything was as simple as you made this! Dave Taylor is the man! I went to other forums and everyone said there was no hope. And it took me 2 minutes with your instructions. Almost took my hard drive back, so thanks again!

Posted by: juxtaPOW at July 17, 2011 6:47 PM

Thanks so much for this, it was a lifesaver!

Posted by: Rachel at August 8, 2011 8:45 PM

Thanks very much. Clear and concise instructions (which work).
Andy

Posted by: andy at September 5, 2011 6:44 AM

I have exact same problem with my new external drive with Mac. I followed the steps to erase but when I click erase it says "Disk erase failed with error: Could not unmount disk" Please help. Thanks.

Posted by: Esra at September 14, 2011 9:19 PM

Thank you, so helpful!

Posted by: Liz at October 17, 2011 9:21 PM

Dave:
This was awesome. I recently bought a Mac and am transitioning all of my files and hit a road block on using my portable drives which were showing up as read only. Your instructions were flawless, thanks so much.

Posted by: Perry Resnick at November 13, 2011 11:09 AM

THANKS A LOT!

Posted by: TJ at November 24, 2011 2:38 PM

THANKS!!! WHY CANT EVERYONE BE CLEAR AND EASY LIKE THIS.

Posted by: V at December 8, 2011 11:02 PM

Just perfect description and problem solving - thanks a lot!

Posted by: Andre at December 9, 2011 1:39 AM

THANK YOU!

Posted by: Melanie at December 10, 2011 7:11 PM

Hi! I just read your article right after I formatted my hard disk into Mac OS X (journaled) and not MS DOS (FAT). And now my windows computer cannot detect the harddisk :( But I need to ask my files now for my assignment. Do you have any suggestion? Thanks

Posted by: Hestin at December 15, 2011 6:03 PM

You just saved Christmas. Thank you!

Posted by: Notorious N-I-K at December 26, 2011 4:40 AM

Thank you so much for your explanation. It helped immensely. Your'e a legend!!!

Posted by: Tasha at December 27, 2011 1:04 AM

This is brilliant! Thank you!

Posted by: crystal at December 31, 2011 12:56 AM

Perfect!!!!
Worked like a charm.
Thanx from Holland.

Posted by: NOYLe at January 1, 2012 1:55 PM

Thank you so much!! That will teach me to not by something that's not included in the apple empire.
Awesome tutorial, easy to follow and we even had the same Harddrive.

Posted by: Mikaela at January 4, 2012 6:37 AM

Thanks so much ! This was soooooo helpful !

Posted by: Tess at January 17, 2012 6:31 AM

This solved my challenge
Was afraid that the device would have to go back to the vendor.
Saved a lot of headaches.
Also, there was a post on the web about a downloadable program that would allow you to use the program free for 30 days and then you would have to pay to write to the drive because their software would stop working.
You have saved a lot of people.
Thanks,

Posted by: Sir Duke at January 28, 2012 3:10 PM

i spend almost 2 hours just to find appl. in mac that can read inf. file. i thought it was the problem because it can use properly in windows..and end with nothing even with wine_bottler. But with your way it just take 2 minut..it is really helpfull. thanks

Posted by: okta at January 29, 2012 5:47 AM

Thank you! This worked like a charm!

Posted by: Barb at February 2, 2012 11:48 AM

Hey Dave,

I recently switched over from a windows to a mac and I have a sizable amount of sound files saved on my external hardrive which is indeed formatted for ntfs. Since I wanted to be able to download more music without sacrificing memory on my new mac (and still be able to use the files I had already saved on the external drive) I knew I would need to reformat the hardrive so I could write on it.

I didn't really want to pay for 3rd party software, I downloaded the 10 day trial version of Paragon's NTFS-3g so I could copy all of the files I had on my external hardrive onto my desktop while I followed the steps you suggested using disk utility to reformat my external hardrive to the Mac OS. When I go to erase the contents of my hardrive using disc utility a message comes up saying that the volume erase failed because it couldn't unmount the disc. Is there any way around this? Or will I be stuck having to pay for the Paragon software to write on the disc? Thanks for your time!

Posted by: Ish Zafer at February 7, 2012 5:07 PM

How to format the hard drive without erasing the data?

Posted by: yagnesh at February 9, 2012 3:51 AM

Yagnesh, I don't understand your question: you can't reformat a hard drive without losing the data. Use a backup, restore afterwards.

Posted by: Dave Taylor at February 9, 2012 6:49 AM

I have something to say, now that you mention it, but ...

I do have a lot to say, and questions of my own for that matter, but first I'd like to say thank you for all your efforts on this Web site by buying you a cup of coffee!

I do have a comment, now that you mention it!