How to format a large external usb hard drive for use between both an OS X Mac and a Windows 10 PC

All versions of Windows since Windows Vista should be able to access a GUID drive. Because OS X is able to partition a GUID partition, we want to partition our large external hard drives with this compatible partition table. So, any modern computer since 2006 should be compatible. GUID doesn’t suffer from the restriction of a maximum partition size of 2TB, so if we have a hard drive larger than 2TB, we won’t be required to build multiple partitions with MBR.

Here’s a good quote for other important features regarding GUID (GPT stands for GUID Partition Table).

“On an MBR disk, the partitioning and boot data is stored in one place. If this data is overwritten or corrupted, you’re in trouble. In contrast, GPT stores multiple copies of this data across the disk, so it’s much more robust and can recover if the data is corrupted. GPT also stores cyclic redundancy check (CRC) values to check that its data is intact — if the data is corrupted, GPT can notice the problem and attempt to recover the damaged data from another location on the disk. MBR had no way of knowing if its data was corrupted — you’d only see there was a problem when the boot process failed or your drive’s partitions vanished.”

exFAT was released in 2006 as well, but Microsoft added backwards-compatibility to previous Windows versions from before Vista. The main benefit to it is that it doesn’t have the file size restrictions of FAT32, so individual files with exFAT can be larger than 4GB each. It probably isn’t super important for smaller files, but it could be a necessity for people working on larger files like videos or disk images.

Below is a step-by-step procedure for formatting a large External USB drive which can be used by both a Mac and a PC. This setup will utilize the newest, most fault-tolerant partition tables, and allows for the largest volume and file size capabilities. In my case I am formatting an 8TB Seagate Backup Plus+ USB 3.0 external HDD hard drive.

First, plug a new USB drive into a Mac:

1. The Mac will automatically prompt if you want to use the drive as a Time Machine backup Disk – click “Don’t Use”
2. Open Disk Utility
3. On the left side of Disk Utility, under External, you should see your drive listed.
4. Select the “highest-level” of the drive, not the partitions located underneath. In my case, Seagate Backup+ Desk Media.
5. At the top of Disk Utility, click the “Erase” button.
6. Name your disk, such as “JC-External”.
7. Under “Format” drop-down menu, select “ExFAT”
8. Under “Scheme” drop-down menu, select “GUID Partition Map”
9. Click “Erase”
10. Once the drive has been erased, again, Time Machine will prompt to use as a backup disk – select “Don’t Use”
11. Click “Done”
12. Your drive should now be listed under Devices in the Finder.
13. Control-click or right-click on the device in the Finder, and click “Get Info”.  You can see that indeed it created an 8TB ExFAT Volume, but the Sharing and Permissions cannot be modified. Permissions can only be set if the drive is formatted with  “OS X Extended”. Also, notice that the Created/Modified dates may not be accurate, however, files and folders contained in the drive will display accurate modified dates/times.
14. One thing to note, is after initially formatting the drive on a Mac, and then attaching the external drive to a Windows 10 PC, the drive may not immediately display with a drive letter by default in the Windows File Explorer. Go into Windows 10 Disk Management and find the drive listed in the discovered drives, but you may find that a drive letter is not associated with the volume.
15. To fix this, in Disk Management, right-click on the large/unidentified new data volume and click “Change Drive Letter and Paths…”. Next, click the Add.. button, assign a drive letter (D:) and then OK. You should now find your external drive listed in Windows Explorer and see the files and folders you copied into it while it had been connected to your Mac.