I understand your reasoning. But it has some problems (which you may decide to live with, which is fair enough):
a) It leaves you vulnerable to a greater risk of filesystem corruption (which is more often than not constrained to one instance of a filesystem, unless you are an FS/device driver developer ;-> ); If you monitor your disks, failed disks sometimes (more often than not in my experience) go through a failure period where some cluster of blocks become inaccessible, before the entire drive crashes. Splitting filesystems reduces the impact and gives greater chance of recovery.
b) OS reinstalls *are* more difficult. Your solution is conditional upon good backups - but backups are easier to set up if you arrange your filesystems sensibly.
c) It makes dual/multi boot harder to implement.
d) Multiple filesystems provide rudimentary quotaring, so one errant user can't fill up the system filesystem, which is usually bad. Then again if your whole household logs in as "Administrator" this point is moot.
I've used all sorts of partitioning schemes, but they always revolve around the separation of user data from program/OS files. No professional sysadmin would do it any other way - it was good practise in the 70's (initially for different reasons) and it still is good practise.
Put in a couple of 40-60GB partitions for OS + spare - that leaves nearly
400GB for "user data", which is going to take a while to fill, even with a digital camera. By then, expect a second 500GB disk to cost 70 quid (as the Seagate Barracuda SATA 300GB does right now).If necessary, use second disk as a decant area to re-layout partitions on first disk, but with 40-60GB for the OS/programs, you are likely to be good for a fair few years unless you install Matlab + Xilinx with every library possible along with everything else going.
Another solution is to use logical volume management, but it depends on the OS support for it and sometimes the simplicity of simple partitions buys extra robustness.
Yes. I remember when 20MB was the dogs :) Doesn't change anything though.
The only practical answer is another disk. Unless one is rich enough to buy a SAIT tape drive and some media which will do about 800GB per tape typically. Several grand for the drive and 100 quid per tape. Ouch.
DVDs suffer from the same problems as CDRs - as in how long are they good for? 1 year, 5 years, 10 years? I don't trust them for the only copy of valuable data.
What I do in my home server is double up on the disks - I have 4. Each disk carries various data (home directories, /vol/ areas, upto about 40% of the disk capacity), the rest of the disk is used as a backup area for data from other disks. Backups using rsync run several times a day automatically. Won't help is the box catches fire, but it guards against disk failure, which I've had twice in 4 years on that server. For the box catching fire scenario, I back up my really important data to a spare disk in my work PC, using rsync it doesn't take long nor use much bandwidth. But an old mouldy PC in the shed/garage with a big disk and a bit of cat5 (even WIFI) would work well too.
Cheers
Tim