Why the first backup takes days
The first time a cloud backup runs it has to send everything. That first upload is called seeding. Home broadband is usually asymmetric: a 300 Mbps plan may upload at 20 Mbps or less. 1 TB at 20 Mbps is 8 terabits ÷ 20 million bits per second = 400,000 seconds, about 4.6 days of continuous uploading before overhead.
After the seed, backups send only what changed, which is usually small. Some backup services offer to seed from a drive you post to them, and some let you limit the upload speed so the rest of the house can still work.
Check your plan's data cap too: uploads count towards most caps the same as downloads.
Seeding time at a glance
Uploading around the clock, with TCP/IP overhead (94.9 %).
| Data | 5 Mbps | 10 Mbps | 20 Mbps | 40 Mbps | 100 Mbps | 500 Mbps |
|---|---|---|---|---|---|---|
| 100 GB | 46 h 49 min | 23 h 25 min | 11 h 42 min | 5 h 51 min | 2 h 20 min | 28 min 5 s |
| 250 GB | 4 days 21 h | 2 days 11 h | 29 h 16 min | 14 h 38 min | 5 h 51 min | 1 h 10 min |
| 500 GB | 9 days 18 h | 4 days 21 h | 2 days 11 h | 29 h 16 min | 11 h 42 min | 2 h 20 min |
| 1 TB | 19 days 12 h | 9 days 18 h | 4 days 21 h | 2 days 11 h | 23 h 25 min | 4 h 41 min |
| 2 TB | 39 days | 19 days 12 h | 9 days 18 h | 4 days 21 h | 46 h 49 min | 9 h 22 min |
| 4 TB | 78 days 1 h | 39 days | 19 days 12 h | 9 days 18 h | 3 days 22 h | 18 h 44 min |
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