The operation will erase all data and your files will be gone for good. Important note: If you have useful files stored on the external drive, be sure to copy or transfer them to another safe place prior to formatting. Just follow this easy step-by-step guide and you’re all set. In this post, I’m going to show you how to format your external drive for a Mac-compatible file system i.e. Apple Mac machines support a different file system. That’s all because it’s been initialized with Windows NT File System (NTFS), which is primarily for PCs. But somehow, macOS doesn’t allow you to write data to the drive. So, you just bought a new external hard drive or a portable SSD and wanted to use it on your Mac.