The best cloud backup services, which are also known as online backup services, help you dodge data disasters. They automatically copy your files to offsite cloud storage servers that can be reached from anywhere.
The fact is that you can't always count on an external hard drive attached to your PC to provide the safest backup. That's because a single theft, flood or fire could cause both your computer and its backed-up files to be lost at the same time. Cloud backup services prevent this from becoming an issue.
All of the cloud-backup services we tested — Acronis True Image, Backblaze, Carbonite Safe, IDrive Personal, SpiderOak One and Zoolz Cloud Backup — protect your data on their servers with industry-standard encryption. They also let you encrypt your data again with your own private key if you choose, but if you lose that key, the service can't help you.
Otherwise, cloud-backup services vary greatly. A few let you back up operating-system files and applications. Some back up smartphones and tablets. Most can back up to a local drive, and some let you share files with other people or provide file-syncing or dead-storage functions.
Because backing up the entire computer for the first time can take days, a couple of these services let you mail in a hard drive with your data on it.
But while some online-backup services let you back up an unlimited number of devices, and others give you unlimited online storage space, none of them gives you unlimited space for an unlimited number of devices.
One last thing: Cloud backup services aren't the same as cloud-based file-syncing services like Dropbox or Microsoft OneDrive. Nor are they archiving services like Box or Amazon Glacier. We explain the differences at the end of this buying guide.
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What are the best cloud backup services?
Our value pick is Backblaze, which gives you unlimited storage for just $60 per year but backs up only one machine (and an external drive) per account. This is the best cloud backup service if you have a single computer and don't want to worry about the details.
Acronis True Image is the best choice for power users, offering a nearly infinite assortment of features and pricing combinations. But it's rather complicated and expensive for the average home computer user.
SpiderOak is famed for its security and encrypts your data with a unique key that only you have. (Don't lose it.) However, it's quite pricey, so get SpiderOak only if protecting your data from prying eyes is your top priority.
Carbonite was once synonymous with cloud-backup software. Its consumer offerings seem affordable but read the fine print: To get anything like iDrive or Backblaze's level of service, you'll have to pay a lot more.
As for Zoolz Cloud Storage, we can't recommend it because the company no longer lists the service on its website. You can still buy a subscription, but it's not clear what you'll get. We're trying to get an answer about what's going on. For now, hold off.
The best cloud backup service you can get today
IDrive offers the most bang for the buck, backing up an unlimited number of machines to either a 5TB ($3.48 for the first year for Tom's Guide readers) or a 10TB limit, which should be enough for most people.
IDrive's upload speeds are fast, its mobile apps actually back up the devices they run on (and recognize faces in photos for easy tagging), it provides a generous file-syncing option and it even lets you mail in a full drive instead of spending days uploading data.
IDrive also keeps old copies of each file forever, which is handy, but you'll have to mind those storage caps. It also has two-factor authentication, which is an essential feature every online service provider should offer.
Read our full IDrive Personal review.
Backblaze is still the cheapest online-storage solution, gigabyte for gigabyte, and it's the easiest to use — you literally can just set it and forget it. We also like the generous restore-my-mail feature and its rapid upload speeds. Backblaze even lets you locate a lost or stolen computer by geolocating the Wi-Fi network it connects to.
But Backblaze is not ideal for anyone who has multiple machines to back up, unless you have nearly unlimited storage needs. In that case, the reasonable yearly cost to back up each machine may be worth it.
Read our full Backblaze review.
Acronis True Image is a disk-imaging program with a cloud-storage component tacked on. But it's no kludge — instead, it's perhaps the most powerful and versatile online-backup solution available, offering mobile-device and social-media backups, syncing and sharing options and even ransomware protection. It even includes a "survival kit" that quickly creates a bootable file-restoration tool.
The downsides are that Acronis can get expensive, has a confusing pricing structure and doesn't back up external or networked drives.
Read our full Acronis True Image review.
Carbonite says it offers unlimited storage, but you'd better read the fine print, as it doesn't automatically back up large files, external drives, or any kind of video file, on its lowest pricing tier. To get those functions, you'll have to trade up to the point where Carbonite Safe is no longer competitive.
Multiple machines are supported on a single account, but each costs as much as the first. On the plus side, the software is attractive and easy to use.
Read our full Carbonite Safe review.
SpiderOak was the first online storage (or online-syncing) service to make sure the customer held a private, exclusive encryption key. Most other cloud storage services now offer the same thing, but SpiderOak also has strong file-sharing and -syncing features, as well as support for unlimited machines and, if you insist, backups of system files and applications.
Yet SpiderOak's storage-space pricing is so high that it's more competitive with Dropbox than it is with IDrive, and while its file-restoration speed was amazingly fast, its initial upload speed was glacial.
Read our full SpiderOak One review.
Editor's note: Zoolz no longer mentions its cloud backup service for consumers on its website, yet still seems to take orders for it. We're trying to get an answer from Zoolz about exactly what kind of cloud backup solutions it now offers to home users. Until then, we can't recommend this service.
Zoolz has a lot of features and an attractive, easy-to-use interface. The service permits multi-user accounts, lets you back up applications and system files and, at least at the time of this writing, is appealingly priced.
But its Achilles' heel is that the Zoolz servers are just rented space on Amazon's Glacier dead-storage service, which is agonizingly slow to access. It doesn't help that the Zoolz mobile apps are next to useless.
Read our full Zoolz Cloud Backup review.
How we test the best cloud backup services
We took into consideration several factors: storage costs, ease of file restoration, computer-resource usage, unique features and ease of use and of installation. Upload speed also matters, because while your initial backup happens only once, the backup can take days or even weeks if it's several hundred gigabytes.
We give bonus points to those online backup services that let you mail in a hard drive full of data to start the process or send you one to restore your data.
Our testing and evaluating was done on a 2017 15-inch Apple MacBook Pro booting into Windows 10. Mobile apps were run on a Google Pixel XL 2 running Android 8.1 Oreo. We monitored data-transfer rates on the MacBook with GlassWire, and CPU usage using Windows' built-in Resource Monitor.
Each cloud backup service was tested individually, then uninstalled from both devices before the next test. The test set of files to back up consisted of 16.8GB of documents, photos, videos and music. We uploaded this data to each service's cloud servers, then restored a 1.12GB subset of these files to the laptop.
The testing environment was a home in Middleton, Wisconsin, provisioned by TDS Telecom Extreme 300 Fiber internet service. Internet speeds during testing were typically 280 megabits per second (Mbps) down and 120 Mbps up, according to Speedtest.net.
Online backup vs. online syncing vs. online archiving
An online-syncing service's software creates a cloud-based mirror of a specific set of files or folders on your device, and pushes out identical copies of those files to all of your linked devices so that you can have immediate access to them. Think of the syncing service as the hub on a spoked wheel, with all your linked devices at the ends of the spokes.
Cloud-backup services are simpler. They continuously or periodically copy all or most of the files and folders on your computer to their own cloud servers. Instead of the spoked-wheel diagram of a file-syncing service, an online-backup service would look like a straight line between your machine(s) and the cloud server.
Your data stays on those remote backup servers until you need it, and with luck, you never will. Most cloud-backup services offer generous amounts of storage for a subscription fee that is much cheaper, gigabyte for gigabyte, than an online-syncing service.
Cheapest of all are cloud-archiving services such as Box or Google Cloud. These let you offload files you don't immediately need to online servers, freeing up space on your hard drive.
Cloud-archiving services can be dirt-cheap, sometimes as little as a few pennies per month per gigabyte, but there's often a fee to download files again. (The assumption is that you will never need to download all the archived files.) Backblaze has its own very affordable cloud-storage service called B2.