How often, how fast
Upstream Internet bandwidth is a scarce commodity, as is computers' computational power. The software we tested all allow various measures of throttling upstream (and sometimes downstream) bandwidth use, but most have poor controls over scheduling active times for backups.
Most of the software lets you choose one or more of these parameters, time of day to start making backups, time of day to stop making backups, how many minutes of idle time before starting a backup, how much processor power to use while backing up, bandwidth limits for upstream traffic, frequency of backups.
Software that looks to start backups when your computer is idle uses either or both minutes of inactivity and CPU usage, as thresholds to start backing up or unthrottle a backup to full speed. Some software lets you set a maximum percentage of CPU usage that the program can occupy, too.
As with other factors, no two backup packages offer the same options. And unlike desktop backup software, you can't schedule different sets of backup files if you wanted, say, a critical set of folders to be archived every four hours, while music and movies are uploaded only on weekends. This is a terrible omission, having been available for local backups since at least the early 1990s, but unfortunately common to all the tested offerings.
Jungle Disk offers the closest option: you can set up multiple backup volumes, which are essentially like folders at Amazon's S3 and Rackspace, and each can have its own backup selection and schedule.
No package lets you set what should be a perfectly common and reasonable schedule: back up outside work hours and on weekends for office systems, and back up during work hours and overnight at home. The closest is SpiderOak, which lets you select days of the week (you can select or omit days, but the software only can start a backup at a particular time of day).
Backblaze and Carbonite lack the ability to schedule or limit backups to specific times of day, and can't monitor a Mac for activity. Both programs let you set some kind of lower usage priority, but it's fixed no matter what time of day or what you're doing. Carbonite's control is simply Lower Priority; Backblaze and SpiderOak at least let you specify network bandwidth. SpiderOak only lets you specific a start time, but not a stop time.
Backblaze has the unique option of testing your connection via its Web site, which then reports the maximum amount of data that you could send per day at the current unthrottled rate. In my case, at the time I tested, it was 13GB. This should be de rigueur for all backup services, since it requires little effort and improves a customer's understanding of how to plan backups. Most services show a status bar or window with progress and an estimate of time remaining.
The other four services let you set a specific network speed for uploading files and blocks; Jungle Disk lets you set the downstream rate as well. CrashPlan can halt backups, running only during a specified period, while iDrive, Mozy, and Jungle Disk only allow throttling to a lower bandwidth rate outside of defined backup periods during idle times. You can throttle to a very low rate, but you can't choose to halt backups.
All of the services have large to moderate room for improvement in scheduling. Filling a broadband pipe during the wrong time, while leaving it empty during idle times, defeats the purpose of Internet backups. Providing a simple structure, allowing multiple entries to tie backup sets to times of day and throughput speeds, would dramatically enhance each package.
None of the services can prioritize backups based on a goal size for a month, either, which can be an issue with bandwidth caps, already imposed by Comcast (250GB per month, inbound and outbound combined), and with other service providers rolling them out in test markets. This would likely affect you only for an initial backup, but hosted backups should reflect the current broadband market's limits.