Seagate GoFlex won't act as Time Machine?

Are using this drive wirelessly or connected to your iMac via USB?

Did you ever use Disk Utility to format this drive to OS X extended format (journaled) with GUID partition scheme?

Is this drive plugged into power and not just getting its power from the computer's USB port?

Perhaps the drive's file structure has become corrupt. Copy the data to another drive and use Disk Utility to erase the drive. Format is Mac OS Extended (Journaled) with Option GUID. Try using Disk Utility/Restore to copy the backup to a new location. Please note that this will reformat the destination partition.

How is the drive formatted

Is the drive formatted as NTFS? Were you using some NTFS driver to allow Mac to write to it on Snow Leopard (Paragon, or Tuxera or something similar)?

If so, the update to Mountain Lion may have rendered the NTFS driver non-functional, and since OSx cannot natively write to NTFS formatted drives you get the "read only" error.

You'll need to either fix the driver you had, update it, or get a new one if that is the case.

Seagate provide NTFS drivers with many models, usually they break after an OS upgrade, could be the case here.

laurencefrompreston wrote:

Paragon NFTS.

That is not a format, it's an add on that is now out of date.

Format the drive correctly, for a Mac, no add ons.

Csound1 wrote:

Seagate provide NTFS drivers with many models, usually they break after an OS upgrade, could be the case here.

Yup.

laurencefrompreston wrote:

Paragon NFTS.

There we go. You may need to update Paragon to work on Mountain Lion. Paragon is a Driver not a Format. It allows Macs to write to NTFS formatted volumes. It very likely stopped working after the update to Mountain Lion.

It's not their problem, you can pay for an up to date copy if you want to, so it's now your problem, just format the drive correctly for a Mac then you won't need it at all.

laurencefrompreston wrote:

. And if it is a problem Seagate don't seem to be aware of it.

Why would they be? Paragon is an unrelated company to Seagate. They make the driver. Again Paragon does not format drives, it allows NTFS drives to be written to on Macs.

As far as Seagate is concerned, the drive works. The third party add-on driver from Paragon is the one that stopped working.

You can get an updated version, or simply format the drive as HSF+ (Mac OS extended journaled), and then you won't need Paragon's add-on.

The NTFS driver is definiltely out of date if you used this to format the drive before upgrading to OS X 10.8.

Just when it became out of date, I am not sure.

Paragon usually will update their driver for every new OS X version. The Paragon NTFS you had maybe for an older version of OS X.

It may have worked for awhile, but some OS X 10.8 update OR something else you may have installed rendered that driver non-functional now.

If you have anything important on that drive, you will need to purchase another hard drive, format it properly for Mac OS X and copy that data to a new hard drive so you can erase and properly reformat your existing Seagate drive for OS X.

OR purchase a large capacity USB Flash drive and save all your important data there before you properly reformat your Seagate drive to use with OS X.

Also, forget just powering the drive from just a USB or FIreWire port.

If your drive has a power block or cord plug this drive into power and let it run on its own indepemdent power instead Of drawing extra power from your iMac's power supply. .

Your iMac isn't a laptop.

Any type of critical backup drive, IMSO, should be running on its own independent power supply and not from the computer's if that option is available.

Good Luck!

Any HDD that is to be used for Time Machine must be formatted Mac OS Extended (Journaled).

http://pondini.org/TM/5.html

https://support.apple.com/en-us/HT202784

Ciao.