How to Create a Dual function External HD

I've just set up my iMac with parallels and I understand that it's possible to have two partitions on an external hard drive to use with each OS, separately.

Apart from asking for confirmation of the above, I would like to arrange the following:

I currently have a 3TB external HD which has 2 partitions both NTFS, 1 x1GB and 1 x 2GB. I would like to keep the 1GB partition 'as is' for Windows use under Parallels, and also (importantly) to retain the contents, and I want to re-format the 2GB partition for the iMac to use for Time Machine.

Is it simply a case of selecting Disk Utility and then the 2GB partition and choose Erase, and then selecting to reformat it as Mac OS Extended (Journaled)?

It can be as simple as that, but you have to consider the following.

It is not a good idea to have TimeMachine backups on the same disk with other data, especially if you want to keep the content of your 1 GB partition .

Your approach is good, except for the idea to have TM mixed with other data. If the disk fails, you will loose both partitions and the data on them.

Best way forward is to get another external HD and use that only for TM backups.

Cheers ... McBie

Yes as McBie suggests two operating systems, two external drives. You can use the same caddy.

Thanks for you advice guys, I'll do it via a separate drive as suggested.