Does backup *have* to be as large as original drive?

[backerupper3160]

I'm upgrading to Leopard and getting ready to set up my external FW drive…but I'm a little confused about how to do it. Assuming everything else is equal (which it isn't), for argument's sake say I only use 40GB on a 160GB HD and have a 250GB external.

If I want to use both SD and Time Machine, what would be the best way to partition the backup? Would the SD partition *have* to be 160GB to match the master (leaving 90GB for TM), or would it be ok to create an SD partition of only say 80GB, leaving TM 170GB (and thus more room to have more backups).

(It's a lot more complicated than this but I'm still trying to figure other things out, like whether I need to create a smallish partition in case I get a new Mac and want to install Windows [I know about partitioning on-the-fly apps but I don't own one yet.]). Any help appreciated.

[dnanian]

The backup only has to be as large as the maximum amount of data you plan to copy (plus about 20% if you want to be able to start up from it). But don't cut it too close.

[davep]

Dave -- This one should be elevated to the FAQ section of the Forum.

Dave P.

[backerupper3160]

Ok thanks.