Replication window & bandwidth calculator
Find out whether replication or restore fits your window over a given link. Enter your data size, link speed, and nightly window — see the initial seed time, daily replication time, effective throughput, and how much margin you have. Runs entirely in your browser.
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- Daily replication time
- 1.5 hrs
- Initial full / seed
- 30.5 hrs
- Daily incremental size
- 0.5 TiB
- Effective throughput
- 100 MB/s
How to calculate a replication window
A replication window is the time available for a replication job to finish — usually overnight, so it does not compete with production load. Whether a job fits is simple physics: the data that has to move divided by the throughput you can actually sustain. Throughput is your link speed derated by real-world efficiency, because TCP overhead, disk speed, and encryption mean you rarely get the full line rate. The first replication moves the entire data set (the seed); after that, only changed data moves each day.
This calculator converts your link speed to a real byte rate, applies an efficiency factor, and computes the seed time, the daily replication time, and whether that increment fits your window. The same math runs in reverse for restores — a useful sanity check against your recovery-time objective (RTO). If the initial seed will not finish in a reasonable time, seed locally or ship a disk rather than sending it over the wire.
Example: 10 TiB over a 1 Gbps link at 80% efficiency sustains about 100 MB/s, so the initial seed takes roughly 30 hours. At a 5% daily change rate the daily replication is 0.5 TiB and finishes in about 1.5 hours — comfortably inside an 8-hour nightly window.
Last updated: 2026-07-06
Frequently asked questions
How long does it take to replicate or transfer a given amount of data?
Divide the data by your effective throughput. For example, 10 TiB over a 1 Gbps link at 80% efficiency sustains about 100 MB/s, so the full transfer takes roughly a day. Only your daily change set moves after the first seed, which is why incrementals usually fit a nightly window even when the initial seed does not.
What efficiency should I assume for my link?
Plan for 70–90% of the rated line speed. TCP overhead, latency, disk and storage speed, encryption, and other traffic all reduce what you actually achieve. Higher-latency WAN links and busy shared links land at the lower end; a clean, low-latency LAN can approach the top of the range.
My initial seed will not fit the window — what can I do?
The first full replication (the seed) is by far the largest transfer. If it will not finish in time, seed it locally to a directly attached target, or ship a physical disk and let only incrementals travel over the link afterward. You can also add parallel streams, throttle competing traffic, or increase bandwidth.
Does this calculator send my data anywhere?
No. It runs entirely in your browser and only encodes your inputs into the page URL so you can share or bookmark a result. Nothing is uploaded, and no account is required.