For the most part, if you have an external hard drive that you would like to use with your Mac, you can simply plug it in and be off and running. However, depending on your intended uses for the drive, you might be better off setting it up accordingly.
First you should determine if you plan on using it only with the Mac OS, or if you are going to be using it with Windows PCs as well, such as Boot Camp on your Mac, Virtual Machine software, or a dedicated Windows PC.
If the former is the case, then for the greatest compatibility you should be certain the drive is both partitioned and formatted to OS X-native formats. This will ensure the drive supports permissions restrictions should you choose to enable them, as well as the proper partitioning structure for services like full-disk encryption.
To do this, open Disk Utility in your Applications > Utilities folder, and run the following routine:
- Attach your hard drive.
- Select the drive device (the item above the volume name) in the sidebar.
- Click the Partition tab.
- Choose "1 Partition" from the drop-down menu.
- Click the "Options" button.
- Ensure "GUID" is the partition scheme used.
- Name the drive and ensure Mac OS Extended (Journaled) is the format used.
- Click the "Apply" button.
When this is finished, the drive will unmount and then remount, and will then be available for use with any Mac system.
If you need to use the drive in a Windows environment (especially with older versions of Windows), then instead of choosing "GUID" as the partition, you can try using "Master Boot Record," but you'll also want to be sure to format the drive with the FAT filesystem rather than Mac OS Extended. This will result in a drive that can be used to transfer files between most operating systems, and is a great choice for most users; however, it will not allow you to encrypt your drive in OS X.
In addition to FAT, you may notice that Apple supports ExFAT as a formatting in the same menu as FAT and Mac OS Extended. ExFAT is a revamped version of the FAT filesystem, the main benefit of which is support for files greater than 4GiB in size. However, this filesystem is supported only in systems running OS X, and natively in Windows 7 and later. Therefore, if you need to use your drive with an older Windows PC, you might consider an alternative to this.
Your last option is the NTFS filesystem, which is not supported natively in OS X but is the most compatible with Windows PCs. If you plan on using the drive with Windows systems and only need to read it once or twice with OS X, then formatting it to NTFS with a Windows PC is your best choice. OS X will be able to read this drive but will not be able to write files to it -- at least not without modifications to the operating system or the installation of third-party tools.
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