10.5: Create a Time Machine size limit for networked disks

I am using Time Machine to back up my MacBook Pro on a Samba drive connected to a Linux machine, per this hint. The thing is that when you use Time Machine, it will fill up your disk with backups. However, since I am using a shared networked drive, I wanted to leave free disk space for other users and keep my sysadmin happy. So, here is how you can prevent Time Machine from filling up your networked disk.

First, when you use Time Machine with a SMB disk, it creates a .sparsebundle disk image to put the backup data into. The disk image has a capacity of 2.75 TB. Since my SMB disk has only 1.5 TB of capacity, the disk image shows that 1.25TB is used and 1.5TB is available. The trick is to create another sparsebundle disk image of a given capacity (I used 300GB) on the SMB disk. Use 'Mac OS Extended (Case-sensitive, Journaled)' as the volume format in Disk Utility. Name the volume the same as the volume used by Time Machine (it should be Backup of computerName), and save it to something like test.sparsebundle.

Then, turn off Time Machine, mount your Time Machine backup image (by opening the .sparsebundle disk image on your SMB disk) and your newly-created disk image and use Disk Utility to 'restore' the Time Machine disk image into your new image. Click on the 'Erase Destination' button in order to allow Disk Utility to make a block copy of your Time Machine disk image. Wait for the process to finish.

Once finished, unmount both images and open a Finder window into your SMB drive. Note the name of the disk image used by Time Machine; it should be computerName_ABC123DEF.sparsebundle, where ABC123DEF is your MAC address. Delete this image, and rename your test.sparsebundle to this name. Then, restart Time Machine. The next time it backs up, you will see that the backup disk image used by Time Machine now has a new capacity (300GB in my case), and Time Machine will not fill up your network disk. It will use no more than 300GB.

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10.5: Create a Time Machine size limit for networked disks
Authored by: rspeed on Wed, Nov 21 2007 at 8:13AM PST

Wouldn't it be much easier to use hdiutil?

hdiutil resize -size 500m -shrinkonly /Volumes/Network_Drive_Name/path/to/timemachine.sparseimage

10.5: Create a Time Machine size limit for networked disks
Authored by: felix-fi on Wed, Nov 21 2007 at 8:14AM PST

Nice trick... but my experience in that using SMB based partition for Time Machine is potentially very dangerous... read my post on apple discussions forum:

http://discussions.apple.com/thread.jspa?messageID=5918065#5918065

(I submitted this as an hint here yesterday, but it did not make yet...)

Meanwhile exercise extreme caution in using TM on SMB.

Basically, the problem boils down to the fact that TM is NOT able to recover freed space on a sparsebundle image... period.

10.5: Create a Time Machine size limit for networked disks
Authored by: felix-fi on Wed, Nov 21 2007 at 8:21AM PST

Just rephrasing the last sentece
"Basically, the problem boils down to the fact that TM is NOT able to recover freed space on a sparsebundle image which is on an SMB partition. period.

Meanwhile... anybody knows why sparsebundle images (created by TM) seem to report being twice as big as the SMB partition they are sitting on ? Weird...

10.5: Create a Time Machine size limit for networked disks
Authored by: dbs on Mon, Nov 26 2007 at 11:02AM PST

Based on your comment I set about testing AFP to a third-party NAS. This almost worked.

The old backups were correctly deleted (according to the log in the Console) but after deleting them I can only see one backup in the Time Machine GUI. The other backups exist properly (at least based on a quick examination) in the sparsebundle, but they are not accessible form the GUI.

This is a bit disturbing. It seems like something is really broken with sparsebundles. I don't know what would have to be different for AFP on a 10.5 machine to make this work.

I will test this later over AFP to a 10.5 machine and see if it magically works there. Otherwise it's back to CarbonCopyCloner for me and my $500 NAS...

10.5: Create a Time Machine size limit for networked disks
Authored by: odaigle on Wed, Nov 28 2007 at 6:33AM PST

Hi,
I have tested this and when TM filled the 50 Gig I had set the .sparsebundle size to, it successfully deleted only one backup to make place for the new one. I did not had the problem you are telling about. However, my backup partition (my SMB networked drive) was not full. It is only the .sparsebundle disk image that was full.

10.5: Create a Time Machine size limit for networked disks
Authored by: stokessd on Wed, Nov 21 2007 at 8:23AM PST

How about actually using the maxsize setting in the defaults file?

defaults write /Library/Preferences/com.apple.TimeMachine MaxSize 81920

Where the size is in Kbytes.

Sheldon

10.5: Create a Time Machine size limit for networked disks
Authored by: diamondsw on Wed, Nov 21 2007 at 8:38AM PST

I didn't know that - thanks! This will make it much easier to use the same volume for Time Machine backups and backups of other systems. I was afraid I couldn't do it because Time Machine would gobble up the whole disk.

By the way, if the size really is in kilobytes (why??), then that's a paltry 80MB you've given it. ;-)

10.5: Create a Time Machine size limit for networked disks
Authored by: stokessd on Wed, Nov 21 2007 at 12:20PM PST

That command is verbatim from other tips on time machine floating around on the net. I use 250gig and 400gig for my wife's and my laptops. Think of the 80 gig as a proof of concept...

Sheldon

10.5: Create a Time Machine size limit for networked disks
Authored by: Herve5 on Wed, Nov 21 2007 at 1:13PM PST

gosh. Just tried here, and TM still announces 320 Gb available in spite of my 100Gb new limitation.
How does it behave for you?
Do I understand correctly that the TM preference pane should now show 100 Gb max somehow? Do I have to reboot?

10.5: Create a Time Machine size limit for networked disks
Authored by: sd on Wed, Nov 21 2007 at 2:26PM PST

no, that is not the same. I have read that this allows to skip files over a certain size.

10.5: Create a Time Machine size limit for networked disks
Authored by: SandManMattSH on Tue, Apr 22 2008 at 10:39PM PDT

Does this work for local disks as well? (ie: external hard drives connected directly by firewire)

10.5: Create a Time Machine size limit for networked disks
Authored by: hughsaunders on Wed, Nov 21 2007 at 10:46AM PST

Time machine seems to obey disk quotas, so you can set a quota for the user time machine connects to the share as.

10.5: Create a Time Machine size limit for networked disks
Authored by: morespace54 on Wed, Nov 21 2007 at 11:14AM PST

Newbie question: How you do that?
Plus, what if the user want to access the drive for any other purpose? Wouldn't that bring an other problem (i.e. TM filling up all the user's available space of the now "quotas'ed drive")?

I want to be able to fill up the drive with anything I'm working on if I want to but stll make sure the whole drive isn't filled with TM backups.

Which of the proposed commands is the better one? The one that set the maxsize in the plist or the terminal one?

10.5: Create a Time Machine size limit for networked disks
Authored by: hughsaunders on Wed, Nov 21 2007 at 4:37PM PST

http://sial.org/howto/osx/quota/
Has lots of good info on setting up quotas on mac os, other operating systems I'm not really sure about..
The problem is that quotas are at disk level, so if your users are connecting to one machine for backup and other purposes, quota wont help you.
As for the solutions suggested above, the plist one is not well understood yet. -There have been reports of it not working and confusion over units.
So that only leaves the dmg soltution until someone comes up with something better...

10.5: Create a Time Machine size limit for networked disks
Authored by: dkssud on Thu, Nov 29 2007 at 1:23AM PST

oki, i tried that in terminal...

defaults write /Library/Preferences/com.apple.TimeMachine MaxSize 471859200
[400GB limit on a 700GB drive]

seemed like it processed...
but now timemachine is not backing up at all...
what's the reset code?
[should have known that before i tried it i know... :s ]
thanks!
:)

10.5: Create a Time Machine size limit for networked disks
Authored by: serj69 on Mon, Dec 3 2007 at 4:04AM PST

defaults delete /Library/Preferences/com.apple.TimeMachine MaxSize

10.5: Create a Time Machine size limit for networked disks
Authored by: dkssud on Tue, Dec 4 2007 at 10:32PM PST

thanks!
:)
it works

10.5: Create a Time Machine size limit for networked disks
Authored by: dkssud on Tue, Dec 4 2007 at 10:31PM PST

Problem fixed in Time Machine and AirPort Updates v1.0
Authored by: adamcr on Sun, Apr 6 2008 at 10:13AM PDT

This problem has now been fixed with Apple's latest Time Machine and AirPort Updates v1.0. Time Machine will now compact the sparse bundle after it deletes an old backup to make sure it has the right amount of free space. I've posted my logs to show the new behaviour.

Cheers,

Adam

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