External HDD is 'Read only' - How to solve this?

Click on the drive, choose Get Info from the File menu, and check the format.

If it's listed as Windows NT filesystem, reformat it as MS-DOS, exFAT, or Mac OS Extended (Journaled) as desired, or install software which allows Mac OS X to write to NTFS drives. New drives(other than those specifically intended for Macs) typically fall into this category.

If it's formatted as FAT32 or exFAT, use the Disk Utility's Repair Disk command on it, or if you don’t need anything on it, reformat it.

If it's formatted as Mac OS Extended, click Authenticate and provide your administrator password, or change the permissions on that specific folder in its Get Info window.

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I have the same issue. This is nothing to do with the external drive.
I have an iMac too and it is still on Yosemite and the same drive works perfectly on that one. The issue is only the MacPro after upgrading to El Captain.

I am having the same problem. My toshiba external hard drive worked perfectly yesterday morning before i updated to el capitan. it had only ever been used on my macbook pro and now it is saying it's formatted as NTFS which has mysteriously appeared in my settings after updating. how do i fix this? i have wedding photos i need to access to edit!

same problem - can it be fixed by re-installing yosemite?

Hi, I tried installing this driver (http://www.seagate.com/in/en/support/downloads/item/ntfs-driver-for-mac-os-maste r-dl/)

It did solve the issue for me. Very easy and no compromises.

Cheers...

Surya i downloaded this but before installing, will it work with my Toshiba drive?

Hi Niel, can you please help me telling me how I can reformat my HDD from Windows NT filesystem to MS-DOS or exFAT

Or which software would you reccomend to install so my Mac OS Yosemite can write to NTFS drives?

Thanks