Time Machine and Linux Dual-boot

I have a 2011 Mac Mini with OSX 10.7, 8 Gb Ram and 500 Gb hard drive with 114 Gb of usage. I have been using time machine, with an external HD which has 300 Gb total, 180 Gb used. Now I have installed an Ubuntu 12.04 dual - boot configuration. It is likely that I will be switching to the Ubuntu partition primarily but anticipate some secondary usage to continue with the OSX. I propose to partition the external HD to 180/120 with the 180 used for Time Machine and 120 for backup from the Ubuntu partition. I would welcome comments on whether that would be a good plan.

Edit : I would further propose to delete the existing time machine data and start from scratch, presuming that would get me to 114 Gb of 180. I see no need to retain the earlier data.

thanks
tim

I always used individual drives for different OS's had 3 at one time for OSX,Win 7 and Ubuntu it lowered the chance of one drive dying and taking out all 3 backups.

osxx said:

I always used individual drives for different OS's had 3 at one time for OSX,Win 7 and Ubuntu it lowered the chance of one drive dying and taking out all 3 backups.

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I had considered that myself. I think that is a good idea. I've got other drives here.
Thank you

That's not only a good idea, it's really the only way you really should do it without screwing up that external drive with two different files systems on it....

[solved]

chscag said:

That's not only a good idea, it's really the only way you really should do it without screwing up that external drive with two different files systems on it....

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Heard, understood. And implemented! Thanks