Data Transfer Time Calculator

Time = data size / effective speed. Data is usually measured in bytes and links in bits, so the calculator multiplies terabytes by 8,000 to get gigabits first.

Efficiency is the share of the link speed you actually get. Protocol headers, TCP behavior over distance, encryption, disk speed at either end and other traffic on the link all eat into it. 85% is a fair default for a clean LAN copy. Long-distance or many-small-file copies can land far lower.

Moving 10 TB over a 1 Gbps link at 85% efficiency:

• Data: 10 TB x 8,000 = 80,000 Gb
• Effective speed: 1 x 0.85 = 0.85 Gbps
• Time: 80,000 / 0.85 = 94,118 seconds, about 26.14 hours (1.09 days)

The same copy over 10 Gbps takes about 2.6 hours, if the disks at both ends can keep up.

Use the Backup Capacity defaults: 20 TB today, 15% annual growth, one-year horizon, 5% daily change, 14 daily points, 5 weekly, 12 monthly and 3 yearly fulls, 2:1 reduction and 15% overhead. The model gives 23 TB protected at the horizon and a 273.76 TB provisioned repository.

That repository estimate is not the amount sent each night. In this example, 5% of 23 TB is 1.15 TB of changed data. Enter 1.15 TB, 1 Gbps and 85% efficiency in Transfer Time: about 3.01 hours. A 23 TB full copy at the same speed takes about 60.13 hours.

The time model does not know your backup software's actual wire bytes, changed-block behavior, source disk speed or restore performance. Use measured job statistics to replace the example inputs. Test restores separately.

At full speed, 1 Gbps x 86,400 seconds = 86,400 gigabits, or 10.8 TB. At 85% efficiency it is about 9.2 TB.

Often the bottleneck is somewhere else: a single slow disk, a busy backup target, VPN encryption, or high latency limiting a single TCP stream. Running several copy streams in parallel often helps.

The calculator uses decimal TB (1,000,000,000,000 bytes), matching network speeds that are also decimal. Your operating system may show the same data as about 9% fewer TiB.