Cloud backup
How long will my first cloud backup take?
Short answer: divide the amount of data by your upload speed, not your download speed. 1 TB at 20 Mbps up takes almost five days of non-stop uploading; at 300 Mbps it takes under eight hours. Backup apps usually leave headroom for the rest of the house, so expect the real figure to be 10–35% longer than the table below, and plan for the first backup only. After that, only new and changed files go up.
Upload time for a first backup
Times assume the upload runs continuously at 95% of the measured upload speed (the same allowance for protocol overhead our download time calculator uses). 1 GB = 1,000 MB, the way backup apps and drive makers count.
| Data | 10 Mbps | 20 Mbps | 35 Mbps | 100 Mbps | 300 Mbps | 940 Mbps |
|---|---|---|---|---|---|---|
| 100 GB | 23.4 h | 11.7 h | 6.7 h | 2.3 h | 47 min | 15 min |
| 500 GB | 4 d 21 h | 2 d 10 h | 1 d 9 h | 11.7 h | 3.9 h | 1.2 h |
| 1 TB | 9 d 18 h | 4 d 21 h | 2 d 19 h | 23.4 h | 7.8 h | 2.5 h |
| 2 TB | 19 d 12 h | 9 d 18 h | 5 d 14 h | 1 d 23 h | 15.6 h | 5.0 h |
How the numbers are worked out: 1 TB = 8,000,000 megabits. At 20 Mbps × 0.95 = 19 Mbps, that is 8,000,000 ÷ 19 = 421,053 seconds, about 117 hours or 4 days 21 hours. The columns run from low upload tiers on DSL and cable to symmetrical fiber.
Why the backup app is slower than your speed test
- It throttles itself on purpose. Backblaze, for example, documents that its Automatic Throttle "attempts to limit the rate at which the Backblaze software uploads files to 70%-90% of your total connection speed" so other activity is not disrupted (Backblaze performance settings).
- It may use one connection. The same page notes that Backblaze "typically" uploads over a single connection and that adding threads can help when latency stops one connection from filling the line. Speed tests that open many connections at once will show a higher figure than any single-stream upload can reach; our test uses one connection, so it is closer to what a backup sees (see our methodology).
- Small files are slow. Thousands of photos or documents cost more per gigabyte than one large video, because each file has its own setup and checking.
- The computer sleeps. An upload that only runs while the laptop is open can take three times longer than the table.
Check your data cap before you start
Uploads count toward monthly data limits. Xfinity, for example, says that on its older plans with a 1.2 TB monthly limit "almost all internet activity counts — anything you stream, download, upload" (Xfinity 1.2 TB data plan FAQs). A 1 TB first backup plus normal streaming can push a household over such a limit in one month. If your plan has a cap, either spread the first backup over two billing months by selecting folders in stages, or check whether your provider offers an unlimited option first.
How to finish faster
- Back up the irreplaceable folders first: photos, documents and project files. System files and apps can be reinstalled.
- Let it run overnight, plugged in and on a cable. Wi-Fi in a far room can cut upload more than download.
- Raise the app's speed limit at night and lower it during the day. If the house's calls start freezing while the backup runs, that is latency under load; a router with SQM lets the backup run flat out without hurting calls.
- Check you are getting the upload you pay for. If the speed test is well below your plan's upload figure, work through why upload is slow before blaming the backup service.
- For very large data sets on slow upload, some services offer seeding by shipping a drive. Compare that with the table: 2 TB at 10 Mbps is close to three weeks.
Related
Download and upload time calculator · Mbps to MB/s converter · Download vs upload speed · Why results change between runs