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10.5: Store different files on different Time Machine drives System 10.5
I love Time Machine, but I still think it's incomplete. I'd love to be able to back up different stuff to different disks: this way, when I'm home I could back up the whole system on my large 500GB external drive (as I use a PowerBook), and when I'm on the road, I could back up only some relevant folders on my external 30GB hard disk. With Time Machine, you can back up to different disks, but you can't back up different stuff to different disks.

Before reading on, please understand that the following might be dangerous to your data: please back up on a different disk before proceding. I am not responsible for any data loss you might encouter; this hint has only been tested by me! You should also know that this hint causes (I still don't know why) the deletion of the data contained in the folder /.fseventsd/. I thought this would cause a big mess, but everything seems to work fine so far.

With those warnings in mind, read on for my solution...

Let's say you have two disks: BigDisk and SmallDisk. And let's suppose that you want to back up the whole system to BigDisk, and only some really important folders on SmallDisk. Connect BigDisk and set Time Machine to use it. I went for manual backups, but I don't think this changes anything), then back up (with Time Machine off, to start a backup, you have to right-click on Time Machine icon and select Backup Now). When you're done, unplug BigDisk and go to /Library/Preferences.

Copy the file to a safe place and name it Plug in your LittleDisk, and set up Time Machine, excluding all the folders you think are of no vital importance. Once again, I selected manual backups and I started a backup. When it finished, I copied the file (it has changed now!) to a safe place and named it

Now let's say you want to back up again to BigDisk. Here's what you need to do:
  • Close the Time Machine preferences pane!
  • Unplug LittleDisk and plug in BigDisk
  • Copy and rename the copy to
  • Replace /Library/Preferences/ with the file you just created
  • Open the Time Machine preferences pane, select "Choose another disk," and select BigDisk (and again, I selected manual backups)
You can now back up! The same procedures applies if you want to BigDisk from LittleDisk. On my PowerBook, everything seems to work perfectly. The only thing I noticed is that the size of the folder /.fseventsd/ shrinks everytime I switch from BigDisk to LittleDisk: maybe some developer out there can explain why, and whether this is dangerous.

[robg adds: As I understand it, fsevents is what lets Time Machine do what it does -- it keeps track of all filesystem changes in real time. However, I don't the importance of that directory and its contents.]
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10.5: Store different files on different Time Machine drives
Authored by: Sven G on Dec 18, '07 08:08:22AM

Interesting hint...

BTW, if you also have a .Mac account, a quick-and-dirty way of backing up the whole system *and* your home folder - or whatever subset of it - could be to use Time Machine for the whole computer and .Mac's just for your home folder: thus, redundant backups with little effort, and both automated if you wish so.

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re: 10.5: hacking Time Machine
Authored by: mclbruce on Dec 18, '07 06:12:01PM

The beauty of Time Machine is that there are few decisions for the user to make. Once they point it at a hard drive and turn it on, the user is done. Just about the only thing that can be done to mess up Time Machine is to turn off the backup hard drive.

The more choices the users have, the more users will make bad choices. To Apple, that means more support headaches, more customers who lose data and blame it on Apple, and maybe even some class action lawsuits. If they are smart Apple will keep Time Machine as simple as possible.

It's one thing to risk your own data by hacking Time Machine. That's fine with me. But, disclaimer or not, the author is encouraging others to risk their data using his hack by publicizing it here.

I think the only reason for anyone to follow this hint is if they are too cheap to buy a better backup system than the one that comes with Leopard. That's not very good reasoning in my opinion.

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10.5: Store different files on different Time Machine drives
Authored by: dfbills on Feb 03, '09 07:36:56PM

I suspect that the fsevents registry shrinks because it purges information about the drive when you eject. If this is the case, the only side effect would be that your next backup (after remounting the drive) is that it will require "deep traversal" and the scan for updated files will take longer.


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