Currently Being ModeratedJul 28, 2012 5:48 PM (in response to jeffanon)
I don't need weekly backups from several years ago.
Then just sit back, relax and let Time Machine do its job. You certainly do not need to buy a new drive if you still have stuff that old in your backup, as Time Machine will start removing old files from the backup. It will remove files that either no longer exist in the present or that have been modified more recently. It will make space available as necessary, as long as the backup drive is at least 2-3 times larger than what you're trying to back up, and will always leave you with at least one full backup.
Currently Being ModeratedJul 28, 2012 5:55 PM (in response to jeffanon)
The "weekly backups from several years ago" will disappear. The Time Machine Preferences window points out that "The oldest backups are deleted when your disk becomes full."
After doing a backup, I think that's when TM checks through to see if there are hourly backups older than a day that should be removed (the first is kept as a daily?) and if there are daily backups older than a month that should be removed (the first daily in a week is kept as a weekly). So some snapshots are removed at that point.
When TM is about to do a backup, it works out an estimate of how much space it will need on the TM volume. If that much space is available it goes ahead. Otherwise it goes into a cycle where it deletes the oldest backup and checks again how much space is available.
Note that an old backup might not actually be taking up much space: only the data that is changed between it and the next-oldest backup. So if you put a huge amount of data on your disk, the next TM backup could take ages while it deletes lots of old backups, gradually getting enough space.
I have seen situations where ALMOST ALL the TM snapshots were removed in order to make space for new data. Admittedly this isn't always the action you want, but the bottom line is that TM gives priority to newer data. If I know I'm shuffling temporary data I either put it into one of the folders I've told TM to ignore (e.g. I have a "tmp" folder under my home dir for this) or I temporarily turn off TM.
If you've put many GB of data onto your system temporarily and TM included those in a series of backups, then eventually when the last of those are old enough to be removed (either because they were just hourly or daily and didn't make it into a weekly snapshot, or because they're in a weekly that's getting removed in search of new space) then when that last copy is removed the free space on the TM volume will take a big jump upwards. Until then they'll just sit there chewing up space.
Currently Being ModeratedJul 28, 2012 11:57 PM (in response to jeffanon)
Thomas and dburren,
Many thanks for giving me what I had not found in the Apple article. I'm feeling a lot better about my backup situation now.
Currently Being ModeratedJul 29, 2012 12:03 AM (in response to jeffanon)
You can also delete specific files / folders that have been backed up. Go into TM and right click on any file/folder and choose the option to get rid of that from all backups. Whilst you don't usually need to do this, it can be useful if you've accidentally backed up e.g. a huge virtual machine file and want to reclaim the space to allow your other backups to be held longer before the drive fills and prunes older backups automatically.
Currently Being ModeratedJul 29, 2012 3:39 AM (in response to jeffanon)
If you find you have other questions about Time Machine, take a look at this site:
The guy who writes the stuff on that site knows just about everything there is to know about Time Machine!