How does Time Machine decide what to delete when its disk gets full?

Time Machine deletes the "oldest" backups when it needs more room for a new backup. But exactly what does that mean? Does it delete the oldest backups for the disk being backed up? Or does it delete the oldest backups across all source disks?
For example, if I back up N Macs to a single drive until it is nearly full, what happens when I add the N+1th Mac and start backing it up? Will it remove some existing files to make room for the new disk's backup, or will it just say "no more room"?
The answer to this question will affect my choice of backup disks to purchase.

If you're backing up multiple Macs to a TM backup Volume then if the TM Volume's free space becomes exhausted and TM cannot find room for the current backup it will start trying to delete the oldest backup snapshots associated with the Mac being backed up. It will not touch backup snapshots for the other Macs.
After 37 days all TM snapshots will be weekly snapshots (with a Sunday date). So if you've been running TM for 37 days or longer there will be one or more weekly snapshots. TM will start with the oldest weekly snapshot and start trimming away to make more disk space available.
TM is supposed to alert you BEFORE it starts deleting oldest snapshots but at this time it will perform these deletes silently and as much as it can and then only if there's insufficient space will it tell you it has deleted old snapshots but there's still insufficient space for the backup

Similar Messages

How Does Time Machine Help If... iCal Data Lost?

Hi,
How does Time Machine help if, say, your iCal database gets messed up? Or, how does it help if you accidentally delete all your playlists from iTunes? I'd be interested to know.

That's a very good question (although probably better directed at Apple than us). Because Time Machine is new and Apple's in house programs handle data in different ways, there are a range of different means of recovering data for different applications. Not very user friendly and iCal is one of the least user friendly ones.
As an experiment, because I don't make much use of iCal and have no real idea how it works, I tried to find out how to restore its data. Starting with working with the application: nope, not TM aware at present. OK, where does it restore its data? Next step Spotlight where, as it happens, the obvious search "Calendars" brings up a folder in ~/Library labelled that with a whole lot of mysterious stuff in it. I'm pretty sure that restoring that folder would do the trick. No doubt, if you could figure out which Calendar belongs to what in the above folder you could restore a single calendar that was causing problems. Still, Apple's clearly got some work to do to make this more transparent. Roll on iCal4!
(By the way Mail also restores from within the program).

How does time machine work when being used with a mac pro?

How does time machine work when backing up a mac pro?
Considering the fact that the mac pro can hold 8TB and a external (non NAS) hard drive can hold only 2TB does time machine only backup the OS disk.

macnewcomer22 wrote:
Considering the fact that the mac pro can hold 8TB and a external (non NAS) hard drive can hold only 2TB does time machine only backup the OS disk.
Time Machine will backup everything by default, on every disk in your Mac.
Choose System Preferences > Options to exclude items. You could exclude everything except your OS...but I'd think it is your data that's more important to you, if you have to make choices.
See...
http://discussions.apple.com/thread.jspa?threadID=1964018
While it's true you can store almost 8TB, how much do you think you'll actually store? If you have 1TB of data you want to store then a 2TB drive can do it. Also when your TM drive begins to get full it will begin deleting the oldest backups to make room.
You could also get a Drobo with 8 bays...
http://www.drobo.com/products/index.php
-mj

How does time machine back up separate but computers on the same drive

Thinking about hooking up a hard drive to APBS to use as a time machine for several macs /iPads, how does time machine keep these different devices separate? How does it keep the backup info separate? Thanks

APBS is usually called AEBS or Airport Extreme Base Station.
You can only do Time Machine to the newest one.. it is not supported on earlier models.
See http://pondini.org/TM/Home.html
Look for Gory details about airdisk.
Also it is going to help you to actually read how Time Machine works on network drives.
What you are asking has all the answers there.
http://pondini.org/TM/Works.html
ipads do not backup like macs.. there is no time machine.
ipads backup to itunes or to icloud. The backup to local itunes can then be backed up by TM to the disk you are using.
Please note even though Apple now says it works.. I have seen reports where the old problem has come back.. it works for 6-8weeks and then the backup corrupts itself and you have to start over.

Does not say "The oldest backups are deleted when your disk becomes full."

I am helping someone set up her backup, but I noticed that in the Time Machine window, there is no line that says: "The oldest backups are deleted when your disk becomes full."
She is running Mac OS 10.5.8, on a 2.66 GHz Quad-Core. Her first backup ran fine, but we're concerned that it will not delete older backups automatically to make space.

It works differently in Leopard and Snow Leopard.
In Leopard, the box is titled +Warn when old backups are deleted,+ and Time Machine will fail with a message when it runs out of room and that box is checked.
On Snow Leopard, the title is +Notify after old backups are deleted,+ and that's what happens -- the old backups are deleted, then you get a notice.
See #C4 in Time Machine - Troubleshooting (or use the link in *User Tips* at the top of this forum).

How does Time Machine handle disconnected external media drive ?

I have an external drive connected to my iMac, and backup to a Time Capsule.
I prefer not to keep that external media drive connected all the time...
When I disconnect that external media drive and Time Machine runs, does TM perceive this as "deleted"?
With that drive disconnected, does TM then "release" the prior media drive backup and replace it as it needs space?
When I reconnect the external Media Drive, does TM see it as "new" or recognize it as the prior data and (presuming it's not over-written it) simply manage it incrementally?
Ultimately - do I need to either ensure that the external media drive is always available to use TM, or do I run the risk of screwy / uncertain behavior if it is sometimes present, sometimes not.
Gosh I hope that was clear for you experts out there ;-)
D

an external drive backed up to a TM would forever be retained in the TM... never flushed,
Correct. Except.......if the backup drive is close to becoming full, Time Machine will start to delete the oldest backups to make room for new backups.
So, if you have been backing up the external drive for the last year, and the backup drive is running out of space, you may not be able to go back a full year in Time Machine to see exactly how the external drive looked a year ago. You might only be able to go back 10 months, for example, instead of 12.
Most users really don't ever need to go back more than a few weeks or maybe a month or two to pick up a file that they might have accidentally deleted, so the fact that you might not be able to go back a full year or more to see how the drive looked at that time in the past, is not really that important for most users.
Most of us need to know that we have a complete, up to date backup of the external drive in case it fails.
Time Machine will warn you whenever it starts to delete the oldest backups, so if you really do need to be able to go back a year, or two years, or however long it has been since you originally started to back up the external......and you don't want Time Machine to start deleting the oldest backups of the external to make more room.....then you will need to add another backup drive and start backing up everything to that new drive.

How does Time Machine Handle separate Boot and User Volumes?

I recently installed an SSD and set it up as my boot drive, and I'm using another hard drive for my Home folder, if I ever run into a scenario that I need to restore my entire system, how will Time Machine handle it?
Will it restore my system back to the drives that they came off of?, in other words will my Boot volume be restored back to the SSD and my Home folder back to the hard drive, or will it restore everything back on the one disk it asks me to select before I click restore?

Michael Hoover wrote:
Ok, so if I tried to access a backup from booting with the Snow Leopard install disk I won't be able to select which volume I need to restore?
You would restore the OSX volume via the procedure in #14 of [Time Machine - Frequently Asked Questions|http://web.me.com/pondini/Time_Machine/FAQ.html] (or use the link in *User Tips* at the top of this forum).
You would restore the data-only volume separately, via the "Star Wars" display, per #15 in the FAQ.
I guess I would be better off doing incremental backups with Carbon Copy Cloner on 2 partitions on the same volume.
That would also take two separate operations to restore. (It would be a good idea to do such backups +*in addition+* to Time Machine backups, in case there's a problem with either disk drive or backup app, or a user error like erasing the wrong disk.)
Your scenario is actually quite unlikely; you'd rarely need to restore both volumes at once. If the SSD fails, you'd only need to restore it; if the HD fails, you'd only need to restore that.
It would get a bit more complicated if you get a new Mac, especially one with a single volume. That's one of the reasons it's a good idea to keep at least a minimal Admin account on the OSX volume.

How does Time Machine handle multiple profiles?

Hello,
I have an IMac with 3 users, does time machine handle all users?
2 users are admins, but when i change users the time machine does not handle well the external drive.
Can you give some info in this matter.
Thanks
Nuno

It should work fine. All of my machines have multiple users. What problems are you having?

HT201250 How does Time Machine allocate backup data.

I have over 150GB to back up with time machine and only 256GB HD to use, does Time Machine back up all files each time or only files updated after the last backup?

Time Machine first makes a full backup, and then, it makes incremental backups backing up only the files that have changed since the last backup. When the Time Machine drive gets full, Time Machine will start deleting old backups in order to be able to make new backups. If you want more information about Time Machine, see > http://pondini.org

How does time machine use the external disk space??

does time machine back up only the changed or new stuff or does it back up everything? does this mean that if on "day one" it backed up 600 gb worth of data, the next back up on "day 2" would be 600gb+a few more things, or would it be 600gb+600gb+the few more things? Does it back up "day one" in a whole package and "day two" in another package, or does it back up "day one", plus only the different things made from "day one" to "day two""?
similarly, does it keep stuff from the first back up ever, plus anything new or modified in the following back ups, then when it is full, does it let just the oldest files drop off? or does it drop off everything from the initial backup? that is, if I had 20mb of changes would it erase only 20mb of data to make the new data fit, or would it erase all 600gb from say "day one"?
thanks for the answer!
iMac, Mac OS X (10.6.8)
<Email Edited by Host>

See Pondini's TM FAQs for starters.

How does time machine handle deleted files

I've recently grown into a 1.5TB external hard drive where I back up my iMac through Time Machine. I'm a photography hobbyist who does a lot of processing work on my photos in Photoshop, therefore I'm regularly generating sizable data to back up.
My question is, using some hypothetical numbers:
Pretend I create 50GB of new data by importing a lot of photos onto my iMac, then Time Machine does it's thing before I can decide what photos I want to keep or trash. I later go back and edit my photo catalog and decide I only want to keep 1/2 of photos from that previous import, reducing that data to only 25GB. Will Time Machine keep those old pictures on my external drive, even though I deleted them from my iMac? Will Time Machine ever recognize I threw away those files, assume I don't want them, and overwrite them? Or is Time Machine going to keep using my my external drive to back up everything until I used up all of the externals space?
Message was edited by: Michael Streubert

Understanding how TM deletes things can be difficult, but I'll try to summarize it:
-TM will back up your system every hour.
-After 24 hours, TM will delete all but one of the 24 previous hourly backups. The one it decides to keep will become your "daily" backup. You have no control over which of those 24 backups it will select to keep as the daily.
-After 30 days, TM will start to delete the old daily backups too. It will keep 4 of the last 30 backups, one for each week.
-After your TM disk fills up, it will start to delete old backups to make room for new ones.
So, after you delete them from your main HD, the length of time that they kept on the TM drive can vary. If the files existed for only a few hours, then there is a good chance that they will be purged from the backups the following day. Or they might be kept for weeks or months, depending on if TM decided to keep those backups as the daily or weekly. It's kind of a crap shoot.
If the files existed on your main hard drive for between one and seven days, then they will remain on your TM backup drive for at least a month. After that they are at risk of being purged out.
If the files existed for more than a week, they will stay on your TM drive until it fills up. After that, they are at risk of being deleted.
I hope this helps.

How does time machine work, and what does it really do?

i just got my macbook pro, and just wiondered what time machine does, and how t works

Hi p,
Basically, it's an incremental, hourly backup application (you provide the HD). After the first backup, it only backs up new/revised data (plus some overhead), so it takes up much less space than all separate backups. Some reading for you:
Basics: http://support.apple.com/kb/VI29
How to back up and restore your files: http://support.apple.com/kb/ht1427
Recovering Your Entire System
http://docs.info.apple.com/article.html?path=Mac/10.5/en/15638.html

How does Time Machine handle large files?

I'm relatively new at the whole Time Capsule / Time Machine process and have learned that large files (eg aperture library) are backed up each time there is a change and this can lead to the TC filling up quicker than normal.
How does this work with daily and weekly backups?
For example, if my aperture library is, say 1Gb and I import a load of photos from my camera and this goes up to 2Gb. I've learned that I should disable time machine while I'm in Aperture (or at least before 10.6...not sure now). So given I've done that, imported the files to Aperture but want to edit them later and ultimately move them into iPhoto to keep the Aperture album small.
When I turn back on Time Machine, the next hourly backup will know the library has changed and will back it up, this will go on until a day backup has been taken - this deletes the 24 hourly backups? or does it merge them?
If I then do the editing the following week, then export the photos and the library is now back to 1Gb again....backed up hourly/daily/weekly etc what am I left with??
Do I have an original, the 2GB version and the new 1Gb version...ie 4Gb......is there a cunning way I can work to change the files within a week so only one of the changes is in the backup?

Orpheus999 wrote:
When I turn back on Time Machine, the next hourly backup will know the library has changed and will back it up, this will go on until a day backup has been taken - this deletes the 24 hourly backups? or does it merge them?
The Time Machine panel of System Preferences says this:
Time Machine keeps
- Hourly backup for the past 24 hours
- Daily backups for the past month
- Weekly backups until your backup disk is full
Each time Time Machine runs it creates what appears to be an entirely new backup set, although it does this in a way that doesn't require it to copy files that have already been copied. So merging isn't necessary. Another effect of how it operates is that each unique version of a file (as opposed to packages of files) only exists on the backup volume once.
According to the contents of my Time Machine backup file, hourly backups are literally kept for 24 hours, not until the next "daily" backup. For a "daily" backup, it seems to keep the oldest "hourly" backup for a day.
If I then do the editing the following week, then export the photos and the library is now back to 1Gb again....backed up hourly/daily/weekly etc what am I left with??
Do I have an original, the 2GB version and the new 1Gb version...ie 4Gb......is there a cunning way I can work to change the files within a week so only one of the changes is in the backup?
You might be able to exclude those files from being backed up at certain times, but I can't be sure this would result in older copied of those files being retained.

How does Time Machine track changes?

My Leopard upgrade got stuck with a minute to go - I had to hold down the power button to restart my Mac, but to my surprise Leopard launched and everything seemed to work fine. I set up Time Machine and it's been running without problems, backing up to my 2nd internal drive. The only problem I noticed was that a few hidden files weren't hidden - presumably it hadn't finished cleaning up after itself. So, I carried on using Leopard until today when I finally decided it might be a good idea to run the installer again. The installation completed fine, and everything is running nicely.
My question is: will time machine track any changes that have been made from re-running the installer, or does it only track changes that are made while Leopard is running? Should I switch off Time Machine, delete the backups, and start again, or will it handle these changes?

When I log back into 10.8 Mountain Lion and Time Machine does it's normal back up thing, does it recognize changes that were made to internal disks, folders, and files that were made when I was previously booted into 10.7 Lion?
Yes.

How does time machine handle initial backup after upgrading to Yosemite?

HI All,
I'm wondering if Time machine will create a "new" full backup of the system after I upgrade to Yosemite.
I'm trying to make sure I can backout (revert to previous backup of Mavericks) of the upgrade should I run into trouble.
Thanks,
Eddy817

besides restoring just one file, that is what Time machine DOES. See this article:
Time Machine - Frequently Asked Questions -- 14. How do I restore my entire system?
If you are deeply concerned, you may want make a copy of your entire system before updating (Clone your old system) or Install onto a Blank drive and add your files to that.
If you make NO preparation and do not have a Backup, the only way to install a previous versions is to do so onto a Blank drive. Also, you must have PURCHASED (even for $0) a copy of Mavericks, or it will not be available for re-download.

How does Time Machine decide what to delete when its disk gets full?

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