Understanding throughput to size your network
Bits or bytes, disk or network: how to compare throughput, estimate how long a backup takes and size a network without a bottleneck.
Also available in Français
We often see infrastructures that are well equipped with servers and storage… but held back by their network. Understanding throughput is essential to avoid bottlenecks, especially during massive backups or data transfers between sites.
Bits, bytes: the basics
- 1 byte (B) = 8 bits (b).
- Network speeds are generally expressed in bits per second (e.g. 1 Gb/s).
- Disk and file transfer speeds are expressed in bytes per second (e.g. 150 MB/s).
👉 Result: 1 Gb/s ≈ 125 MB/s in practice.
Throughput comparison table
Here is a simple table to better visualize the typical speeds of disks and networks, with their English and French equivalents:
| Technology | Typical throughput | Equivalent in MB/s | English term | French term |
|---|---|---|---|---|
| HDD 7200 rpm (14 TB) | 1.2–1.6 Gbit/s | 150–200 MB/s | Hard Disk Drive | Disque dur |
| SATA 6G SSD | 4–4.4 Gbit/s | 500–550 MB/s | SATA SSD | SSD SATA |
| PCIe 3.0 x4 NVMe SSD | 24–28 Gbit/s | 3000–3500 MB/s | NVMe SSD | SSD NVMe |
| PCIe 4.0 x4 NVMe SSD | 40–56 Gbit/s | 5000–7000 MB/s | Gen4 NVMe SSD | SSD NVMe Gen4 |
| 1 GbE network | 1 Gbit/s | ~125 MB/s | 1 Gigabit Ethernet | Réseau 1 Gigabit |
| 2.5 GbE network | 2.5 Gbit/s | ~312 MB/s | 2.5 Gigabit Ethernet | Réseau 2,5 Gigabit |
| 10 GbE network | 10 Gbit/s | ~1250 MB/s | 10 Gigabit Ethernet | Réseau 10 Gigabit |
| 40 GbE network | 40 Gbit/s | ~5000 MB/s | 40 Gigabit Ethernet | Réseau 40 Gigabit |
Concrete example: a 1 TB backup
Let’s imagine a 1 TB (≈ 1000 GB) backup to transfer to a backup server. Here is how long it takes depending on the network:
- 1 GbE network (125 MB/s max):
1000 GB ÷ 125 MB/s ≈ 2h15 - 10 GbE network (1250 MB/s max):
1000 GB ÷ 1250 MB/s ≈ 13 minutes - 40 GbE network (5000 MB/s max):
1000 GB ÷ 5000 MB/s ≈ 3 minutes
👉 You can see the problem: on 1 GbE, a simple backup can take hours, and during that time your network is saturated.
The bottleneck
A key principle to remember: the final speed always depends on the slowest link.
Let’s take an example: you need to back up 4 TB of data.
- With NVMe SSDs capable of 3500 MB/s, a pure disk-to-disk copy could theoretically be done in under 20 minutes.
- But if your network is only 1 GbE (≈ 125 MB/s real), the transfer drops to:
4000 GB ÷ 125 MB/s ≈ 9 hours. - With a 10 GbE network (≈ 1250 MB/s), the same backup would only take:
4000 GB ÷ 1250 MB/s ≈ 53 minutes.
👉 The takeaway: your disks can be ultra fast, but if the network is too slow, it will bottleneck overall performance.
How to size intelligently?
- Assess your data flows: how many TB of backup each night, how many VMs replicated, what transfer times are acceptable.
- Compare disk and network: make sure the network doesn’t throttle the disks, and vice versa.
- Plan for headroom: with data growth, it’s better to slightly oversize.
- Segment your usage: separate production traffic, backups and replicas to avoid overall saturation.
Conclusion
Properly sizing network throughput is just as critical as choosing the right servers.
I help companies audit, optimize and modernize their network and storage infrastructures. The goal: ensure your backups complete on time, without saturating your critical flows.
📩 Unsure about sizing your network?
👉 Get in touch: Arthur Perrot, infrastructure & cybersecurity expert.