When comparing rsync vs Backblaze, the Slant community recommends Backblaze for most people. In the question“What are the best backup apps for Mac OS?” Backblaze is ranked 2nd while rsync is ranked 4th. The most important reason people chose Backblaze is:
The default configuration includes everything except for system files to be backed up. That also includes external USB drives. This will work for most people. It can, of course, be customized to each person's liking.
Specs
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Pros
Pro Fast and bandwidth efficient
Only the changed parts of files are synced. For instance, if a long log file increases by just a few lines of text, a small diff will be sent to and saved in the archive. Rsync also compresses data in transit.
Pro Works over SSH
SSH support allows sending files securely over the network by encrypting all communcation.
Pro Pre-installed on OSX and most Linux distributions
Many *nix systems bundle rsync so there's nothing to install. All you need to do is open up the terminal and start using rsync.
Pro Free and open source
Licensed under GNU.
Pro Beginner-friendly defaults
The default configuration includes everything except for system files to be backed up. That also includes external USB drives. This will work for most people. It can, of course, be customized to each person's liking.
Pro No file size or traffic restrictions
There are no limitations of file size or amount of data you can upload. The $5/mo plan gets you unlimited cloud storage.
Pro Excellent restoration performance
Backblaze creates a zip file of all your files for you to download, thus decreasing the amount of data you need to download and increasing the speed of the download since it's one connection instead of multiple that need to be opened and closed for a list of files.
Pro Secure
AES encrypted files are transferred over a secure SSL connection.
Pro Download any backed-up files from any web browser
Some backup services like Carbonite require a client to be installed to restore files. Backblaze allows you to login and download any or all files from a web browser, meaning it also serves as an ad-hoc cloud storage platform.
Pro Users can order a physical copy of their data
You can have a flash drive or an external hard drive delivered to you. They cost $99 and $189 respectively.
Cons
Con No official GUI
To use rsync, you have to know your way around the command line.
Con Complicated, and you can accidentally overwrite the wrong files
Con No Linux support
There's no Linux client for Backblaze.
Con Pay extra to keep deleted files permanently
Additional $2/Month plus $0.005/GB/Month for files updated, changed, or deleted more than one year ago.
Con Backblaze does not support network (NAS) drives
If you use a thing like Drobo, Backblaze will not back it up.