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This weekend I launched a backup that lasted longer than expected, meanwhile the cron start another remote backup of the same host, resulting in killing the previous backup that was more critical.
As a suggestion, can you include a switch to stop a backup if another is running in the same machine, only notifying on the log and leaving us the choice?
Since version 10.3.2 process management has changed to be less agressive with ongoing jobs. In any case, you fell into a backup job design flaw, you should be using backup job chaining to prevent this kind of situations. Use --on-success and --on-error arguments to launch subsequent backup only when the previous has finished.
Note: running two backups at the same time will not last as the sum of running them subsequently, it will take much, much longer, and only if you are lucky to have decent hardware, cause you might very well clogg your server up to a point in which it just says "I had enough". We won't delve into the details of why this is as is, although many of you have that clear.