Inputs
Example Data Table
| Scenario | Backup type | Source (GB) | Change (%) | Compression | Dedup (%) | Net throughput (MB/s) | Allowed (h) | Estimated (h) | Status |
|---|---|---|---|---|---|---|---|---|---|
| Branch file server | Incremental | 2,000 | 5 | 2.5 | 30 | 106.88 | 2.00 | 0.37 | OK |
| Virtualization cluster | Full | 3,000 | — | 1.8 | 20 | 178.11 | 2.00 | 2.52 | Overrun |
Formula Used
1) Data to protect (GB)
- Usable = Source × (1 − Excluded%)
- Incremental data = Usable × Change%
- Full data = Usable
2) Data after reductions (GB)
- AfterCompression = Data ÷ CompressionRatio
- AfterDedup = AfterCompression × (1 − Dedup%)
3) Effective throughput (MB/s)
- Candidate = PerStream × Streams × Efficiency%
- SharedCap = min(Network/8, TargetWrite)
- Raw = min(Candidate, SharedCap)
- Net = Raw × (1 − ProtocolOverhead%) × (1 − EncryptionOverhead%)
4) Total time (seconds)
- TransferSeconds = (AfterDedup × 1024) ÷ Net
- FixedSeconds = (Setup + Catalog + Verify) × 60
- TotalSeconds = TransferSeconds + FixedSeconds
How to Use
- Select Incremental for daily deltas, or Full for total copies.
- Enter the source size and any excluded percentage.
- For incremental runs, set a realistic daily change rate.
- Adjust compression and dedup based on observed ratios.
- Enter performance limits: per-stream, streams, network, and target write.
- Add fixed step times for snapshots, cataloging, and verification.
- Press Submit and compare estimated time to your allowed window.
- Use the download buttons to share results with your team.
Backup Window as a Capacity Budget
Treat the backup window as a nightly capacity budget. The calculator converts protected data, change rates, and reduction ratios into an estimated transfer volume. That volume is then divided by the effective bottleneck throughput, plus fixed operational steps. This lets engineers compare required hours against the allowed maintenance window and adjust inputs to match reality. Include setup, catalog, and verify minutes to prevent surprises later every cycle.
Reduction Ratios Drive Real Transfer Volume
Compression and deduplication are multiplicative, not additive. If 20% of data is excluded, 1.5× compression, and 2× dedup are applied, the transferred set can shrink dramatically. Use measured ratios from recent jobs, because synthetic benchmarks often overstate savings. When ratios are uncertain, run scenarios with conservative and optimistic values to bound risk. For new datasets, start with 1.2× compression and 1.3× dedup.
Throughput Is the Minimum of Several Limits
Effective throughput is the minimum of per stream speed times stream count, network capacity, and target write speed. Shared networks need concurrency adjustment, because other jobs consume bandwidth. Protocol and encryption overhead further reduce usable throughput. This calculator explicitly applies those percentages, making the impact visible. If your estimate fails, identify which limit is lowest and relieve it first. When using WAN links, test latency effects on stream efficiency.
Fixed Steps Matter When Data Gets Smaller
Snapshot creation, cataloging, and verification can dominate when deltas are small. Ten minutes of setup is trivial in a ten hour full, but huge in a forty minute incremental. Enter the best available averages, and keep them separate from transfer time. If verification is optional, compare outcomes with and without it, then document the operational risk. Record these steps in runbooks so teams can forecast change.
Using Results to Improve Reliability
Compare the estimated duration to the allowed window and compute buffer. A 20% buffer helps absorb retries, slower links, or unexpected change spikes. If buffer is low, consider more streams, faster targets, staged backups, or more aggressive exclusions. Track actual job duration weekly and recalibrate ratios. Consistent inputs yield dependable scheduling and fewer missed restores. Export CSV or PDF to attach assumptions to change requests.
FAQs
What is a backup window?
A backup window is the allowed time period to complete backup processing. It includes data transfer plus fixed tasks like snapshots, cataloging, and verification. The goal is to finish before production workloads or service-level policies require systems to be fully available.
Which size should I enter for incremental backups?
Use the protected dataset size, then provide an estimated daily change rate. The calculator converts that rate into an incremental data amount before applying exclusions, compression, and deduplication, giving a practical transfer volume for nightly runs.
Why does the estimate change when I add more streams?
Parallel streams can increase throughput until another limit becomes dominant. Network capacity, target write speed, or overhead can cap gains. If the bottleneck is not per-stream performance, additional streams may yield diminishing returns.
How do I choose overhead percentages?
Start with measured observations from your environment. Protocol overhead often ranges from 2% to 8%, while encryption can add 3% to 12% depending on hardware acceleration. Use conservative values if you have limited telemetry.
What buffer should I aim for?
Many teams target 15% to 30% buffer between estimated duration and the allowed window. Buffer absorbs retries, contention, and unusually high change days. If you operate across WAN links, consider a larger buffer.
Do the exports include my inputs and results?
Yes. The CSV and PDF exports capture the main assumptions and computed results. Save them with change tickets or runbooks so future adjustments are based on documented inputs rather than memory.