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Time Machine Question (Delete old backups?)

F

follicle

macrumors newbie
Original poster
Sep 6, 2007
12
0
Hello,

I am currently using Time Machine to do backups on my Macbook. I'm not really interested in being able to restore my Mac back to a certain date – I'm only concerned with backing up my hard drive contents.

My question is: If I am doing backups weekly, can I just delete the previous week's backup after backing up tonight? I mean, tonight's backup will contain all of the same files that last week's did (including any new files and excluding any deleted files).

Am I right, or do I need to keep all of my back ups?

Thanks!
 
follicle said:
Hello,

I am currently using Time Machine to do backups on my Macbook. I'm not really interested in being able to restore my Mac back to a certain date – I'm only concerned with backing up my hard drive contents.

My question is: If I am doing backups weekly, can I just delete the previous week's backup after backing up tonight? I mean, tonight's backup will contain all of the same files that last week's did (including any new files and excluding any deleted files).

Am I right, or do I need to keep all of my back ups?

Thanks!
Click to expand...

Time Machine is smart enough to only backup what has changed. So if it hasn't changed since last week, it won't be backed up tonight.
 
Jason S. said:
it won't be backed up tonight.
Click to expand...
Not true, it will still back up regardless of change or not. (which I doubt given he has been using his computer for a week)

However, like Jason said, it is true that it will only back up new files. I see no reason why you would need to delete the old backups. They're there just in case and not taking up much space.
 
angemon89 said:
However, like Jason said, it is true that it will only back up new files. I see no reason why you would need to delete the old backups. They're there just in case and not taking up much space.
Click to expand...

Actually, tonight I compared the size of last week's backup and this week's back up. Last weeks was about 50 GB. This week's was 52 GB.

Apparently, TM backs up only what has changed, but creates a new folder with all of the non-changed items in it as well.

I wouldn't delete them, but my external hard drive isn't that large, so I would run out of space relatively quickly if I didn't. I just wanted to know if it would be all right.
 
Ok, now I'm really confused.

I just found out how it works. Time Machine performs an initial back-up. After the initial back up, any additional back-ups will contain all of the same files, EXCEPT, Time Machine will create links (aliases) to the initial back-up of any files that haven't changed since the last back up. I deleted the last two back-ups I performed, including my initial back-up, so this lead me to believe that since many of my files haven't changed, the current back up on my drive was useless – just a bunch of dead links. I was wrong...

I plugged the drive into another computer and tried to pull up some files. No problem at all. If I deleted my "initial back-up" then how on earth can I view files on the drive that are supposed to be linked to that initial back-up?

It doesn't make sense... :(
 
I guess I'm missing the part about why you are so concerned about this. If your back-up HD becomes full, Time Machine will delete your oldest back-ups to make room for the newest.

The whole point of Time Machine is having all of this managed without you having to worry about it. Just let Time Machine do its job, and you'll be fine. :)
 
Time Machine will delete older backups when space is needed. Just let it do its thing and leave it alone.
 
Jason S. said:
Time Machine is smart enough to only backup what has changed. So if it hasn't changed since last week, it won't be backed up tonight.
Click to expand...

Your answer seems to contradict itself. If time machine isn't smart enough to backup only what has changed, then EVERYTHING would get backed up every time. Not, as you say, unchanged items don't get backed up.
 
follicle said:
Ok, now I'm really confused.

I just found out how it works. Time Machine performs an initial back-up. After the initial back up, any additional back-ups will contain all of the same files, EXCEPT, Time Machine will create links (aliases) to the initial back-up of any files that haven't changed since the last back up. I deleted the last two back-ups I performed, including my initial back-up, so this lead me to believe that since many of my files haven't changed, the current back up on my drive was useless – just a bunch of dead links. I was wrong...

I plugged the drive into another computer and tried to pull up some files. No problem at all. If I deleted my "initial back-up" then how on earth can I view files on the drive that are supposed to be linked to that initial back-up?

It doesn't make sense... :(
Click to expand...

In a UNIX file system, the file and its name are two different things. A file can have one or several name entries in directories within the file system. All those name entries are hard links. The "first" name given to a file is no different from other hard links created to it. The file will stay on the disk until all hard links to it are removed. When that happens, the actual file space will be reclaimed by the file system.

If you open a terminal window and do the command "ls -l" in a directory, the number in the second column shows the number of hard links to the file.

By using hard links, Time Machine can do a backup every hour and create a full directory tree of your entire system very quickly and only copy the files that are actually changed.

In most cases, doing a backup every hour or once a week will consume roughly the same amount of space.

Time Machine is designed to do backups without user intervention and will delete old backups when the disk space run low. I think it works best if you don't tinker with it.
 
pesc said:
Time Machine is designed to do backups without user intervention and will delete old backups when the disk space run low. I think it works best if you don't tinker with it.
Click to expand...

I have multiple machines connected to a single 500GB TM. Will each instance manage their disk space? In other words, it will not overwrite the other TM threads on the disk?

My concern is that my disk, after TMing all my Macs is nearly 70% full (just a lot of data I guess). Is this okay too?
 
ux4all said:
I have multiple machines connected to a single 500GB TM. Will each instance manage their disk space? In other words, it will not overwrite the other TM threads on the disk?

My concern is that my disk, after TMing all my Macs is nearly 70% full (just a lot of data I guess). Is this okay too?
Click to expand...

It is OK to backup several machines to the same TM volume. Each machine will create its own top-level directory and they will not touch each other.

When TM starts a backup, it will check how much disk space it thinks it needs. If the target volume cannot hold that much data it will delete old backups. I believe it will only delete old backups for its own machine though. I'm not sure if TM has any special mechanisms to balance multiple computers if they compete for disk space.
 
rdowns said:
Time Machine will delete older backups when space is needed. Just let it do its thing and leave it alone.
Click to expand...

That's what I thought but then TM told me I was out of disk space. I reformatted the disk and started again which fixed. So what happened?
 
Mako5 said:
That's what I thought but then TM told me I was out of disk space. I reformatted the disk and started again which fixed. So what happened?
Click to expand...
Time Machine will give a warning before it deletes old back-up files. That does not mean that it cannot back-up anymore, It's just warning you that doing so will result in the oldest back-ups being deleted.

I believe that it defaults to this notification. If you prefer, you can change this in preferences.
 
overcast said:
Because your TM drive was not large enough for one full backup of your source drive.
Click to expand...

Yeah this happened to me. Only b/c I don't use Time Machine enough, so each of my backups got bigger and bigger, rather than incremental backups. It's best to backup often so you'll have a lot of backups that don't vary in size. So then you won't get the not enough space error b/c it can't back up your latest.
 
pesc said:
In a UNIX file system, the file and its name are two different things. A file can have one or several name entries in directories within the file system. All those name entries are hard links. The "first" name given to a file is no different from other hard links created to it. The file will stay on the disk until all hard links to it are removed. When that happens, the actual file space will be reclaimed by the file system.

If you open a terminal window and do the command "ls -l" in a directory, the number in the second column shows the number of hard links to the file.
Click to expand...

That's very useful (to me anyway) thanks Pesc, as I didn't know this about Unix.

Does anyone know, can you use more than one external drive for TM. For instance once a month I'd like to do a full backup to a drive and then keep it at my Mums, whilst still having another drive at home for daily backups.

The reason for this is if there is a fire/burglary (God forbid), then at least I would have a backup off-site.
 
Super Duper rocks if you just want a single backup of your system.

Where Super Duper doesn't rock is when you need to restore a file you accidentally deleted three months ago and then realize that your Super Duper backups only go back to last week.
 
aristobrat said:
Super Duper rocks if you just want a single backup of your system.

Where Super Duper doesn't rock is when you need to restore a file you accidentally deleted three months ago and then realize that your Super Duper backups only go back to last week.
Click to expand...

This is a valid point. If you feel like you want to either have different version floating around so you can restore to previous version, or if you may delete something that you later on realize that you want, TM is the way to go. For myself, I keep my files quite organized and don't delete anything unless I know I am done with it.
 
PowerBookRelic said:
This is a valid point. If you feel like you want to either have different version floating around so you can restore to previous version, or if you may delete something that you later on realize that you want, TM is the way to go. For myself, I keep my files quite organized and don't delete anything unless I know I am done with it.
Click to expand...

it is a good point. the program you want to use is up to you, but Time Machine is useful if you do delete files you might need. as for me, I do what you do, only deleting the file if I absolutely know that I am done with it, which is why I can use superduper and get away with it :)
 
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