Mac – Prevent Time Machine From Resizing Disk Image

It turns out my particular problem wasn't covered by other, similar cases, so I'm going to post my own answer describing the actual issue I had, and the solution I found to it.

In my case it appears that somehow my last "complete" Time Machine backup was in fact corrupted somehow; when I looked inside it I found that the contents of my user folder were missing, so Time Machine was in fact correct in thinking that it needed to backup everything from my user folder again.

To solve this I needed to delete the last "complete" backup on my Time Machine drive. To do this I opened my Time Machine volume in the Finder, and navigated inside the Backups.backupdb folder, my computer name and then found the folder with the most recent time and date. After taking a quick look at some of the largest folders I saw that my user folder (the biggest on my system) was empty.

To fix this problem I then ran the following command in Terminal:

sudo tmutil delete "/Volumes/Time Machine Backup/Backups.backupdb/MyComputer/2014-10-01-175432"

Of course you will need to replace the part in quotes with the correct path to the corrupted backup. You can also do this easily by instead typing sudo tmutil delete (with trailing space at the end) and then dragging the folder onto the Terminal window to have it add the path for you (it may include backslashes, this is normal). You'll need to run this command using an administrator account and enter its password, since only an administrator can alter Time Machine's backups.

For anyone experiencing a similar issue to what I was seeing, I would now highly recommend giving your latest backup a quick check to make sure that you aren't experiencing the same problem I was; although the chances of this corruption occurring seems extremely low (Time Machine would have to be forcibly interrupted or crash for it to occur, though having your Time Machine volume disconnect may do it), it doesn't take long to give your latest backup a quick check, but it can save you a lot of time before you go ahead and try other possible solutions.

If you aren't experiencing the same problem I did then I recommend trying the following links:

• Time machine wants to backup too much
• TM is doing a full backup for no good reason
• My backups seem too large

This is a bad idea on a Time capsule. It is possible, but it will be extremely slow to set up and very slow in use.

See Pondini's Time Capsule Q3

You can use Disk Utility to create a custom-size disk image (normal, not sparse) and specify it to be 800GB size, but you have to create that empty 800GB file locally first, then upload it to your Time Capsule. The Time Capsule's disk and network connections are not built for speed.

Even if you reserve 800GB of space on your Time Capsule, there is no quota to shared the remaining 1200GB fairly between your users.

For example - One user could repeatedly fill their SSD with junk, back it up to the Time Machine target on the Time Capsule, delete the local junk and download fresh junk to the SSD. They could repeat this until the 1200GB space is used up. Only at that point would their oldest junk be automatically deleted from their Time Machine history. The other user would not be able to prompt any clear-out of the junk, they would only be able to lose their own oldest material.

Shorter answer: Time Capsule is great, but it is a backup device not a NAS: it is too slow and has no NAS functions. Don't try to use it like a proper NAS. It is handy for storing a few shared files like a very very basic NAS can, but that is very limited.