WD 4TB My Book Duo Desktop RAID External Hard Drive - USB 3.0 - WDBLWE0040JCH-NESN 2-Bay, 4TB Personal Cloud Storage includes 2 x 2TB HDD User-selectable RAID 0/1 or JBOD lets you configure your drive for more speed (default setting: RAID 0), data protection (drive mirroring: RAID 1) or operate as two independent drives (JBOD) High-capacity external storage and backup. Ultra-fast, optimized data transfer speeds. Protecting your data with multiple backup options Complete backup solutions to secure your data from loss - Integrated backup software, Cloud backup with Dropbox, System-level backup;Speed and security with hardware encrypted RAID Formatted NTFS for Windows 10, Windows 8 or Windows 7 operating system. Requires reformatting for Mac OS X