Backup window & bandwidth calculator
How long will that full backup, replication or migration actually take on your link. And what bandwidth do you need to fit it inside the window? Accounts for protocol overhead and realistic link utilization, because nobody moves data at line rate.
Result
Same transfer on other links
| Link | Effective | Transfer time | Fits 8 h window? |
|---|
How it's calculated
Decimal units throughout, as vendors and ISPs use them: 1 TB = 8,000,000 megabits. Transfer time is data × 8·10⁶ / (link speed × utilization). The required bandwidth inverts the same formula for your window, then the table shows the smallest standard link that fits.
The utilization factor is where honesty lives. Line rate assumes zero protocol overhead, an idle network and storage that can feed the pipe. None of which is true at 2 a.m. when backups run. TCP/IP and encapsulation cost 5–10%, backup protocols add their own, and source disks or deduplication appliances are often the real bottleneck. 70% of line rate is a good planning default for a healthy dedicated link; drop it to 50% for shared links or WAN, raise it to 85–90% only if you've measured it.
Two things this model deliberately ignores: compression and deduplication before transfer (if your backup software ships only unique blocks, size the transfer on the reduced amount, not the front-end data), and multi-stream parallelism, which helps you reach the utilization figure rather than exceed it. When the math says the window can't be met, the alternatives are the classics: incremental-forever strategies, source-side dedup, seeding the first full locally, or a bigger pipe.