Selective bootable backup and partition

[londoner]

i want to use my firewire hdd as a vault for all my files. my 80gb powerbook is full, so would like to transfer materials on the firewire hdd and provide relief to the p'book.

but since the firewire (lacie) is only 120 gb, i don't want to create a partition of 80gb on it for SD backup, and then loose the files once i synchronise with the p'book - as many of the files - after the initial backup - would not be on the p'book any more!

i think, in future, you should find a way to create a bootable backup such that , later, we have the option of preserving this bootability feature, yet "copy new or different" files on it only. so that the all the files co-exist. i would love that feature.

i immediately see the impossibility ; you might say if it crosses 80 gb in total then how the powerbook would cope while booting from the firewire.

hence, is it possible to separate this two features:booting and backing up, as follows?

(i) to create a small bootable drive of 4-10 gb [ similar to techtool edrive or protogo ]
(ii) next partition: backup and synchronise - through smart up date such that we have the latest on both
(iii) 3rd partition: files in vault - which will not be deleted but stay as it is , and do not interfere during booting . if needed we can manually transfer those back to the laptop/desktop.

when in crisis: we run just this firewire - WITHOUT plucking more hairs - and SD helps in finding the best solution (given that the firewire has all resources) to restore materials on the internal hdd.

Is it possible to do above - may be in a round about way - with the present version of SD?