Seagate External Hard Drive does not work on Yosemite

It doesn't work for me either. I had installed the Paragon software earlier, so I uninstalled it, restarted my Mac, than re-installed it, restarted my Mac, plugged in the Seagate drive and nothing. So some of us are having a different problem.

I'm experiencing a similar issue with a FW800 External HDD. After installing Yosemite my Mac does not recognize at all the disk; it is not mounted and a warning message says "The computer can not use this disk"

I have no other ways to access the disk: not seen in finder, not seen in Disk Utility, not seen from data recovery apps.

have found in the meantime a solution, in my case I have Seagate external drives.

I have downloaded the Paragon NTFS SW from te Seagate website .

I installed this sw and suddenly I could see and access the external disk.

I'm seeing a similar problem with a "Seagate Backup Plus Drive" not being seen at boot up. I purchased this to be used as Time Machine drive so it's formatted OS X Journaled prior to upgrading to Yosemite from Mavericks. Unplugging the drive and plugging it back int to the USB port seems to "fix" the issue but it kind of defeats having it as Time Machine drive if you expect the backup to "just work.'

This works. You need to reinstall the NTFS paragon drivers available from the Seagate website. Here's the link:

http://www.seagate.com/support/external-hard-drives/desktop-hard-drives/backup-p lus-desk/ntfs-driver-for-mac-os-master-dl/

It did not work for me.

Question. Does the drive show up after the Mac is up and running? I can unplug the drive without the stand are warning (the drive was ejected .. blah .. blah) and plug it back in to the USB port and then it's seen. My issue is a but different as I'm using it as a Time Machine drive and it's formatted OS X Journaled but I opened a case with Seagate and they are looking at the Macbook / OS X as being the problem. I quote:

"If the drive is not showing up on boot in System Report, this would indicate the Mac is not sending a wake up message to the drive. Try different USB ports to see if it is a specific port causing this issue. If you have access to any other Macs running Yosemite, try it there to see if the issue follows the drive or is specific to your computer."

My Seagates are both formatted OS X journaled. I read on another thread if you turn off your Mac, unplug ALL usb devices, unplug Mac for 30+ seconds, plug in Mac and turn on, plug in external drives then open Finder you will see the drives. I have done this and it works BUT the files on the drive won't open for about 10-20 minutes. THEN if the computer sleeps, upon waking the drives have been ejected and are no longer visible.

I ran the link dr.l33ts provided and then had to go to the 'FINDER' on the menu bar select preferences select sidebar and check the external disks check box. That worked for me. Good luck.

http://www.seagate.com/support/external-hard-drives/desktop-hard-drives/backup-p lus-desk/ntfs-driver-for-mac-os-master-dl/

Okay, I followed r3xsy's instructions (downloaded and installed the NTFS driver from Seagate). Then I unplugged all of my USB devices. Unplugged the mac from the wall. Plugged in the Mac to the wall then started. Then unplugged my external from its power source. Replugged in the external into the wall then plugged into the Mac. SO far, it is working, even after sleep and awakening. ONE ISSUE...I cannot copy a file from my Mac drive (SSD) to the external drive.

Here's some tips that might help people still trying to fix this:

1. Run Disk Utility with the USB drive attached. Is it detected? My drive was, but the partition not recognised.

2. If you can detect the partition you can load it directly by clicking on the path (mount point).

3. If you can't detect/access the detected partitions and your drive was formated to NTFS you can uninstall (go to prefereces) and reinstall the paragon drivers: http://www.seagate.com/support/external-hard-drives/desktop-hard-drives/backup-p lus-desk/ntfs-driver-for-mac-os-master-dl/

4. Retry step 2. If that works proceed to steps 5 and 6.

5. Fresh OSX yosemite installs (in my case) reset my finder preferences to not display my external drives in finder window sidebars. Click on the "devices" heading.

6. Also check finder preferences, and make sure external disks options are checked under the "general" and "sidebar" tabs (if that's what you want).

That's pretty much all I can contribute to this problem. If this doesn't solve it or you are formatted to OSX journaled, I don't have any more detailed experience in sorting. Good luck.

My Mac was in sleep over night and upon awakening it this morning the external drives were still visible. YEAH!!!!

I will be attempting to transfer my backed up files from external one hard drive to the other external hard drive then reformat the empty external drive to see if that helps with the communication to my Mac SSD drive.

Fixed. After going through all the usually troubleshooting : reset PRAM , reboot iMac , reboot external GoFlex drive, disk utility - repair , even reformatted the drive and sacrificed two years worth of backup data. All did nothing to make the drive writeable. Drive was readable and was able to copy files off of it prior to reformatting.

Reinstalled the Seagate GoFlex Drive Settings package that shipped with the drive. (A 2TB Firewire 800 Model) and rebooted/restarted the iMac.

The drive and Time Machine are working fine now.

Seems that the desktop adapter required a driver or permission set that is part of the install package.

Again, this needs to be done after the Yosemite Upgrade completes.

dr.l33ts : you are a Doctor. It works perfect. Once i installed it, i just had to restart it and it is there and is working so far.

Thanks.