"Bandwidth control: You might imagine that faster is always better when it comes to online backups, but if your ISP imposes a monthly data cap, you may want the option to limit how fast your backup app sends data to the cloud. For example, if your Internet plan has a data transfer limit of 400 GB per month, some backup apps could max out your monthly allotment in less than two days unless you throttle the bandwidth to a more reasonable speed. On the other hand, if your ISP has no data caps, or if they’re sufficiently generous, you want the fastest possible throughput. Of the services I tested, only Carbonite appears to restrict bandwidth arbitrarily on the server end; the company claims upload speeds of “up to 10 Mbps,” regardless of how much bandwidth your broadband connection offers."
In addition, because upload speed is such an important consideration when you’re backing up to the cloud, I performed a series of timed tests with specially designed files. In particular, I wanted to test a worst-case scenario in which files would benefit as little as possible from compression, thus gaining a better idea of how the services’ apps compared in raw throughput. So I used a Unix utility to create files at various specific sizes (including 1 MB and 1 GB) consisting of completely random binary data, turned off other networking services, and fed my test files to each backup app, timing the upload speed. I timed it myself because the throughput measurements and “time remaining” estimates found in certain online backup apps are notoriously misleading, if not entirely inaccurate. For apps that offered control over network throttling, CPU usage, and threading (that is, sending or receiving multiple chunks of data at once), I performed the tests at least twice: once with default settings and once with all settings cranked up as high as they could go.
When testing upload throughput, I was looking for numbers as close to my broadband connection’s maximum upstream bandwidth as possible. For the most-recent update to this guide, when I retested Backblaze, IDrive, and Acronis True Image 2018, Speedtest.net reported that maximum as 31.62 Mbps. I had conducted my testing of the other apps for a previous update with an upstream connection that maxed out at 22.70 Mbps; however, none of those services came close to that maximum, so I don’t think a faster connection would have made a difference. The highest throughput I measured was 27.1 Mbps, on IDrive with default settings; the lowest was 4.64 Mbps, on Carbonite, which offers no control over throughput on a Mac, and on Windows has only a checkbox to reduce bandwidth.2
Keep in mind, however, that my controlled performance tests may differ from your real-world results, for any of numerous reasons. For example:
Files that are more compressible than the ones I used in my tests may upload faster but also require more CPU power, slowing down other tasks your computer is performing. Compression efficiency also depends on the compression algorithm your backup software uses. There’s no good way to test compression across online backup software: Not all apps report compressed file sizes, and regardless of the test files I chose, your results could still differ wildly—even with the same app—because each file is different.
Software that offers deduplication is likely to back up your data more quickly, and if the deduplication is at the block level rather than the file level, you may enjoy even greater time savings.
Backing up lots of small files (such as all of your saved email from the past decade) can take a lot longer than backing up a smaller number of large files, even if the total size is the same, because each file introduces a certain amount of overhead for scanning, compressing, and encrypting.
Your maximum upstream bandwidth depends on your broadband plan and ISP type, the time of day, network usage by other apps or devices in your home or office, and other variables. But remember: With most home broadband plans, upload speed is much slower than download speed.
Your computer’s processing power can make a big difference in backup speed, because the faster your computer is, the faster compression, deduplication, and other processor-intensive tasks can occur. So the changes you make to your backup app’s settings for CPU and network usage can make a significant difference, too.
Because backing up all the user data from an average computer with an average broadband connection can take days or weeks, backing up and restoring such a large quantity of data for each service I tested was infeasible for me. The main drawback of this limitation was that I couldn’t be sure that my speed results would scale smoothly.