External hard drives have become truly massive; Western Digital, Seagate and others now sell 3TB drives, and Drobo allows up to 16TB of storage to be used in some models.
However, while many of these external storage devices support Firewire or eSATA, many are limited to relatively slow USB2 connections. Some Macs are also limited to USB2, such as the Macbook Air, leaving users stuck with a connection that can only push 30MB/s in an ideal situation. Mac users frequently report even lower speeds while running Mac OS X compared to the same machine running Windows.
While many users can get by with the slower USB2 connection, the bottleneck becomes apparent when large files need to be moved on or off the external drive, or when the user wishes to move all of their files from one drive to another; moving 3TB over a USB2 connection can take almost 2 days. Read more