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According to Apple, Time Machine removes all but one backup for every month, all but one backup for every week of the last month, and all but one backup for every day of the last week.
I have plenty of space on my NAS (about 10 TB), and I'm currently using about 1TB of space, so space is not a concern.
How would I disable this automatic removal of old backups? Or is this impossible for Time Machine and I should use an alternative program such as rsync?
If you want to keep backups that are more regular than weekly, but less regularly than hourly then it's probably best to use a different solution. Time Machine doesn't have these settings (apparently not even in hidden settings).
Time machine keeps weekly backups as space permits. It also stores daily backups for the past month, and hourly backups for the past 24 hours.
In the case that you create a file one day and then delete it about two days later, more than a month passes before you want to recover the file, and the weekly backup that is kept for that time period is not between the time the file was created and the time it was deleted, then a daily backup will keep the file and a weekly backup will not. This is the specific scenario where another backup solution will be desirable. However if you create a file one hour, delete it two hours later, and less than a day has passed, then Time Machine would have the file backed up, but a daily backup is unlikely to have it backed up.
I suspect that you'll find doing hourly backups with rsync will be more intensive for your computer than Time Machine's hourly backups.
