How can I limit the amount of space on a Time Capsule used by Time Machine?

Here is what you can do. Open Disk Util and go to the File menu then New then Blank Disk Image. That will get you this screen.



Name the image what you want and pick a size in the drop down then save it. So in my example this will be a 100MB DMG file. Once you have created the DMG, just double click it in OS X and the image will "mount" in Finder. Once that happens it works like any other disk so you can drag and drop files in and out then eject when done just like an external drive.

Then just copy the file to the TC disk and leave it there. Even is empty the DMG file will keep the 100MB of space available for itself and it cannot be used for Time Machine backups.

Windows won't open this DMG directly, but there are some utilities that add this to Windows. If you search "open os x dmg in windows" you will find some. I have no experience with these utils so can't recommend one.

The sparse bundle is similar, and stores files inside the same way, but it only takes up the amount of space used by the files inside, so won't do the fixed space set aside like you want.

soonerfan237 said:

Is there a way to skip he hassle of using utilities by just creating the disk image from Windows directly?

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There is a utility TransMac that will let you use Windows to create the Mac DMG files, but I don't know why you would bother with it. You just create the DMG file once on the Mac then copy it to the TC where it sits there waiting to be used.

Or maybe I am not following what you are trying to do.

soonerfan237 said:

Basically, I have a Mac with an OSX and Windows partition and I want to back up both partitions to a Time Capsule. I know that Time Machine can't back up both partitions directly so I'm looking for a workaround. I'll use Time Machine to back up my OSX to the Time Capsule. My concern was with backing up the Windows part, but it sounds like I can make it work by creating a disk image on Time Capsule and backing up to that. I was worried that if I created it on the OSX side that it wouldn't be formatted correctly to work with windows. But I don't really know much about this. Do you think this plan will work?

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Okay... now I see what you are trying to do. Limiting space with a DMG like this won't work because the format inside the DMG would need to be NTFS.

But you may be able to just point the Windows backup app to the Time Capsule shared drive and use that as a backup. If used that way the TC will handle any file format issues. But this will not allow you to section of space like you want.

soonerfan237 said:

That sounds like it could work. The sectioning off of space isn't really important to me. That was mostly just a workaround to get Windows and OSX to be able to back up to the same drive. If I don't need to section off space, even better. Do you happen to know if Time Capsule can be used as a shared drive like that?

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I have not done it myself, but when searching I saw some posts from people who have done it.