If I delete files...

...from my MacPro, what happens to those files on Time Machine? I'm trying to free up some space, but I'm not sure I want to permanently get rid of them, just on the Mac.

The file will remain in your Time Machine backup until the Time Machine drive gets full enough that it needs to start deleting old backups. How long it remains after that depends upon how many backups need to be deleted before Time Machine gets to the one that contains that file.

That usually takes a while depending upon size of the drive and amount of data being backed up. If it is something you need to archive long term preserve a copy on something more permanent such as DVDs,

Hmmm. Time Machine does incremental backups, right? That is, the first time, it backs up everything in the Documents folder (only?). Then on subsequent backups, it will only grab anything that was saved since the previous session. If I'm right so far, then only that first backup has any file that has not been modified and saved again. So if it deletes that first backup before a file is opened and saved again, that file is now gone from TM. If you then discover that this file is corrupt, you're out of luck. Did I get that right? This scenario could happen at any point, not just relative to the very first TM backup.

Now, let's say that the default of one back up an hour is in force. Does that mean TM inspects the files somehow, and finding that nothing has been saved since the last backup, it closes without doing a new one?

Sorry, but that's basically all incorrect.
TM backs up everything... There is no documents folder (only) to it, unless you go into the TM preferences and start excluding items from the backups.
It does not save anything that was "saved" since the previous session, it saves everything that "changed" since the last session.

There is no being "modified and saved again" about it.
If you saved a file 2 years ago and started TM backups, never open that file again, don't delete that file from your internal drive and have kept TM backups for the past 2 years, that file that was saved 2 years ago will be in the "current" TM backup - even if the external drive has begun deleting old files. It only deletes files and versions of files that are not now currently on your internal drive. It does not delete anything from the backup that currently exists on your internal drive. TM would be the most useless backup app ever devised if it would delete files in the backup that still exist on your drive.

bobtomay said:

Sorry, but that's basically all incorrect.
TM backs up everything... There is no documents folder (only) to it, unless you go into the TM preferences and start excluding items from the backups.
It does not save anything that was "saved" since the previous session, it saves everything that "changed" since the last session.

There is no being "modified and saved again" about it.
If you saved a file 2 years ago and started TM backups, never open that file again, don't delete that file from your internal drive and have kept TM backups for the past 2 years, that file that was saved 2 years ago will be in the "current" TM backup - even if the external drive has begun deleting old files. It only deletes files and versions of files that are not now currently on your internal drive. It does not delete anything from the backup that currently exists on your internal drive.

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I have attached a screen shot of what is on my Time Machine now. So, if I'm understanding this correctly, when I delete a file on the Mac and then a day or two later decide I didn't really want to delete it, I can go back in "Time" and find it. The latest backup won't have my deleted file, but back a few days will. Is this correct?

Yes. You may be able to go back several weeks or months if necessary depending upon how long it takes to fill your backup drive. Eventually you would reach a point in the future where the oldest backup doesn't have the file you want but for most people that takes quite a while.

At the moment my oldest backup goes to October 2014 for example but that's because I have other data on that drive as well. At one point my backups went back an entire year or more.

Slydude said:

Eventually you would reach a point in the future where the oldest backup doesn't have the file you want but for most people that takes quite a while.

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That's what I was getting at in my scenario. I still don't understand exactly what TM does, but apparently there is the potential of losing a file from the backups without you knowing it. Such a file would be one you want to keep, but don't have to change.

Time Machine gives you a warning when it starts deleting the oldest backups. For the scenario you propose where there is a file that isn't being modified your best bet would be to archive the file on something like a DVD before it is deleted from the Time Machine backup.

toMACsh said:

That's what I was getting at in my scenario. I still don't understand exactly what TM does, but apparently there is the potential of losing a file from the backups without you knowing it. Such a file would be one you want to keep, but don't have to change.

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You would have had to delete that file from your internal drive for it to ever be deleted from the TM backup.
You knew it when you deleted the file from your internal drive.
There is no potential of TM deleting a file from the backup that you did not already delete from the internal drive.
If you don't want TM to delete a file - you simply don't delete that file from your internal drive.
There is potential of the drive you keep the TM backup on dying or other wise losing your data - but TM does not delete files that exist on your drive.

While Time Machine does indeed provide for the possibility of recovering files you have deleted from the drive (go back in time), the TM application is for "backups".

Time Machine is not for storing files you want to keep but don't want on your internal drive any longer. For that, you get 2 more drives - one for data storage of things you want to keep but don't want taking up space on your boot drive and the second to backup that storage drive.

Slydude said:

Time Machine gives you a warning when it starts deleting the oldest backups. For the scenario you propose where there is a file that isn't being modified your best bet would be to archive the file on something like a DVD before it is deleted from the Time Machine backup.

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Oh, absolutely. My Documents folder is also on a flash drive AND online (IDrive). Triple redundancy should be enough. TM is really only for other stuff for me. Although it backs up my Documents folder as well, it would be my last resort if the hard drive, flash drive and IDrive fail me at the same time.

bobtomay said:

There is no potential of TM deleting a file from the backup that you did not already delete from the internal drive.

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Since this conflicts with other information provided in this thread, and I've come to trust the advice of both purveyors of said information, and I don't really know myself, I'll continue with the above redundant copies to stay on the safe side. It really doesn't matter to me how TM works on a practical level. I'm just curious.

bobtomay said:

time machine is not for storing files you want to keep but don't want on your internal drive any longer. For that, you get 2 more drives - one for data storage of things you want to keep but don't want taking up space on your boot drive and the second to backup that storage drive.

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this!! ^^^^^

toMACsh said:

snip

Since this conflicts with other information provided in this thread, and I've come to trust the advice of both purveyors of said information, and I don't really know myself, I'll continue with the above redundant copies to stay on the safe side. It really doesn't matter to me how TM works on a practical level. I'm just curious.

Click to expand...

There is absolutely no conflicting information provided between Slydude and myself.

I have been responding to your posts.
Slydude has been responding to the ops questions. The first one was:

If I delete files on my MacPro, what happens to those files on Time Machine?

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Please note the title of the thread: "If I delete files" part of that question.
That is the question Slydude has been responding to.

Only items that you have deleted from your internal drive, will at some point begin to be deleted by TM when the backup drive begins getting full. That is exactly what Slydude and myself have been saying.

At no point in time will Time Machine ever delete a file from the backup that currently exists on your internal drive unless you specifically go into the Time Machine preferences and exclude items from the backup.

TM is smart.
Any file that exists on your computer will be a part of every single backup that TM makes until you delete the file.
Meaning - a file created 2 years ago, never changed, never modifed, never opened again and never deleted, still sitting on your drive - will be a part of every single TM backup from the first one 2 years ago to the last one you made today - and all while only needing to keep a single copy of the file in the backup.

However, redundant backups are a good thing - I keep both a TM backup and a bootable clone of all our Macs here.
I have triplicate backups of data I really do not want to lose.

(pixeltaker, you've got the right idea there)

Thanks for clearing up that bit of confusion. Summed it up nicely as usual. The key difference in the two scenarios is whether the file has been deleted from the hard drive or not.