How Long Does an External HDD Backup Actually Take?
Moving a large batch of files to an external hard drive always raises the same question: "when will this finish?" For the same amount of data, the time it takes can differ by several multiples depending on the connection type. This calculator takes the file size and transfer method and estimates how long the backup will take to complete.
Speed Differences by Transfer Method
USB 2.0 is the slowest at around 30MB/s, while USB 3.0 is over 3 times faster at roughly 100MB/s. USB 3.1/3.2 can reach 400MB/s, and modern Thunderbolt hits 1000MB/s, moving even huge files quickly. Note that even with a fast port, an older cable will cap the actual speed to whichever component is slower.
Why Real Speed Falls Short of the Theoretical Number
Lots of small files increase the hard disk's seek time, slowing overall throughput. In that case, compressing many small files into a single archive before transferring reduces the number of seeks and noticeably speeds things up in practice.
Frequently Asked Questions
USB 3.0 is theoretically over 3 times faster.
Small files, disk seek time, and cable condition all play a role.
Use modern cables and compress small files into one archive.