Does Arq make bootable backups?
No. For a bootable backup we recommend SuperDuper. Arq is complementary to SuperDuper; SuperDuper creates a bootable backup on another hard drive, and Arq creates versioned backups online.
A bootable backup is a duplicate of your hard drive. It’s great if you need to get up and running very quickly in the event of a hardware failure — you just boot from the backup. But you have to plug in your FireWire or USB drive and update the bootable backup, or it gets out of date quickly.
Arq does versioned backups of the folders you choose. This provides insurance against damaged or accidentally deleted files. A duplicate backup would just copy the damage and delete the same files, but with a versioned backup you can “go back in time” and get the undamaged/undeleted file.
Arq backs up to S3, so there’s no need to remember to plug in a USB drive — it backs up as long as there’s an internet connection. The best backups are the ones that actually get created, after all.
Arq retains versions similar to the scheme used by Time Machine — hourly for the past 24 hours, daily for the past month, and weekly until you reach the S3 budget you’ve chosen in the Preferences.
If you only use Arq for your important files and your hard drive fails, you’ll have to replace the hard drive and install OS X from DVD, and then restore your important files from Arq backups; this would take longer than simply booting from an external drive.