Upgrade from 4.x -> 6.2: Old file systems?

[Brett Glass]

I have a server which I am considering upgrading from 4.11 to 6.2. 
Besides the operating system disk (which contains all of the 
expected partitions such as /, /usr, /var, and /tmp), There's a 
large data disk on the system containing useful data that I'd like 
to put back online as soon as the upgrade is completed. I'd rather 
not have to reformat it unless there is a significant advantage to 
doing so. Does 6.2 work properly with the older disk format? Is 
there any reason to take the time and effort to back up the data 
and restore it to the new format? Is there anything I'll need to be 
careful about if I upgrade just the system disk?

--Brett Glass