TechCompare LogoTechCompare

How long does a 10 TB data migration to the cloud take? WAN latency and the TCP window trap

By TechCompare · Updated · How we check

The 70.6-day result applies to a fixed unscaled window, while 2.2 hours is the ideal link-rate floor with a sufficiently large window. Measure your path before scheduling a migration.

A 10 TB migration over 10 Gbps at 40 ms RTT takes about 70.6 days with a fixed unscaled window of about 64 KiB. The ideal link-rate floor is 2 hours 13 minutes 20 seconds when the window and the rest of the path can sustain 10 Gbps. This is a deliberately constrained example with scaling disabled and a fixed window of about 64 KiB, not a general OS default.

Windows normally enables receive-window autotuning, and Linux enables receive-buffer autotuning by default. A small initial advertised window need not remain a persistent cap.

Transfer time
70d 15h 26m 48s
Window-limited to 13.1 Mbps
File size
10 TB
10000 GB
Link speed
10 Gbps
10 Gigabit Ethernet
Effective throughput
13.1 Mbps
at 40 ms RTT
Link utilized
0.13%
Bottleneck: TCP window
This exact 10 TB copy over 10 Gigabit Ethernet, pre-loaded. Change the file size, link, or model a longer round trip.
Edit in the full tool

How this is calculated

The constrained window ceiling is 65,535 bytes times 8 divided by 0.04 seconds, or about 13.1 Mbps. The bandwidth-delay product is 10 Gbps times 0.04 seconds, or 50 MB. Window scaling allows a receive window that large, but does not automatically select it. Set the modeled window to at least 50 MB (about 48,829 KiB) and verify actual negotiated windows and throughput with a probe transfer.

Verdict

The window-limited scenario is about 70.6 days, not a normal default forecast.

A 10 Gbps link at 40 ms RTT needs about 50 MB in flight to avoid a receive-window bottleneck, and disabled tuning, pinned socket buffers, or blocked scaling negotiation can leave a connection short of that. In this calculator, enable scaling and increase the entered window to model a larger buffer. Storage, encryption, packet loss, and shared-link traffic can still keep the result above the ideal 2 hours 13 minutes 20 seconds.

More WAN scenarios

100 GB over USB 3.0
A 100 GB transfer over USB 3.0 works out to 2 minutes 40 seconds at the interface's 5 Gbps peak rate.
View details
1 TB over USB 3.0
A 1 TB transfer over USB 3.0 works out to 26 minutes 40 seconds at the interface's 5 Gbps peak data rate.
View details
4 GB over USB 2.0
A 4 GB transfer over USB 2.0 works out to 1 minute 6 seconds at the interface's 480 Mbps peak rate.
View details

Related guides

Bandwidth-delay product explained
The concept page that derives the window / RTT ceiling.
View guide
1 TB over WAN at 100 ms latency
The canonical transatlantic 1 TB scenario that proves the 0.5% link utilization.
View guide

Frequently asked questions

How long does a 10 TB cloud migration really take?
At 10 Gbps and 40 ms RTT, a fixed unscaled window near 64 KiB gives about 70.6 days. The ideal 2 hours 13 minutes 20 seconds requires a window of at least 50 MB plus storage and a network path that sustain 10 Gbps. Scaling permits that window size, but does not guarantee it. Measure a representative transfer before planning the migration.
What is the bandwidth-delay product for 10 GbE at 40 ms?
10 Gbps times 0.04 seconds is 400 million bits, or 50 MB (about 47.7 MiB). That is about 763 times a 64 KiB window. Both endpoints must negotiate scaling, and any middlebox must pass the option through. The effective window must actually grow to this size to avoid the modeled limit.
Should I use a physical transfer appliance for a 10 TB migration?
Compare measured network throughput with the appliance's full shipping, ingest, and processing time. This fixed unscaled window example takes about 70.6 days, while a sufficiently sized window on a sustained 10 Gbps path has an ideal 2.2-hour floor. RTT or a scaling flag alone cannot tell you which transfer method will finish first.
Does rsync or SMB Multichannel help with WAN migration throughput?
Parallel TCP streams can increase the combined data in flight when an individual connection is window-limited. Separate rsync jobs or SMB Multichannel can help when supported, but all streams still share the same link, storage, and application limits. Measure the gain rather than assuming it scales linearly.

Related tools

Display Bandwidth Calculator

Check display bandwidth for HDMI, DisplayPort, USB-C, Thunderbolt, and USB4.

Use tool

RAID Calculator

Calculate usable capacity and fault tolerance for RAID 0, 1, 5, 6, and 10.

Use tool

RAM Latency Calculator

Convert DDR3/DDR4/DDR5 timings (CL, tRCD, tRP, tRAS) into true latency in nanoseconds.

Use tool

Memory and Storage Throughput Visualizer

Visualize the large speed gap between CPU cache, RAM, and storage.

Use tool