Linux works very well with disc sizes of less than 1g. There are lots of these older discs around and if you want to make a firewall or other application which doesn't require lots of disc then these are excellent. If you are planning to use a large server then a new disc is a must. As I have said before older discs don't have the checks that modern discs have. There are even modern 20g drives that require you to lockout bad sectors.