The solution I used when couldn’t save files on my Seagate external hard drive from my MacBook Air was to do a partition on my Seagate 1TB external hard drive. If you follow the next steps it will take you 5 minutes to do it from step 3. I hope it helps
1- Connect your external hard drive to your MacBook Air
2- Save all the information you already have on your Seagate External hard drive on your Mac or any other device that allows you to do so.
3- Go to Finder and click on the Applications option from the Favorites section
4- Click on Utilities and double click on Disk Utility
5- Click on your Seagate external hard drive to select it
6- Click on the Partition tab that appears at the top on the right hand pane
7- Click on the Current tab to select how many partitions you want from the drop down (you can select from1 to 16) it is totally up to you.
I will assume you only want 2 partitions
8- Click on the top window (partion1) and give a name on the Name field. I’ll assume you want the first partition is for Windows so you would call it WINDOWS if you want.
9- On the Format field select MS-DOS (FAT) from the drop down.
10-On the Size field Select how many GB you want to reserve for this first partition; I selected 200 GB
11-Now, click on the second window (partition2)
12- Give a name on the Name field. I’ll assume you want the second partition to be Macintosh so you call it MACINTOSH, if you want do the same.
13- On the Format field select Mac OS Extended (journaled) from the drop down.
14-On the Size field Select how many GB you want to reserve for this second partition; I selected 800 GB,
15-Click the Options button to select PC Partition Scheme to enable a partition for use on a Windows computer. Select Master Boot Record.
16-Click on the Apply button
You are done….
