I recently updated to El Capitan 10.11.2 of OSX and within the same day after the OS tried to do a backup on my Time Capsule at home the backup does not work anymore. I have already posted the problem on apple support communities. Backups from other versions of OSX run perfectly correct against the same Time Capsule so don’t let you lure into support procedures like do a clean install….this is a problem with the OS. It seems that the sparesbundle gets corrupted and therefore can only be mounted in readonly mode because there are no more mountable filesystems. Link to the Support Community entry.
If you do not like the aggressive way Time Machine does it’s backups (on an hourly base) you can change this. It is possible to to this by using the command line (terminal). So start the terminal application. On the prompt you can issue a command like this:
sudo defaults write /System/Library/LaunchDaemons/com.apple.backupd-auto StartInterval -int 14400
where 14400 is the interval time in seconds, here 4 hours. If you want to let the backup happen hourly use 3600 and so forth. If you don’t like the command line, you can use the free tool TimeMachineScheduler.