As always Gary explains the "whole ball of wax" in a clear, efficient manner... or as with software "the whole ball of yarn"; dual boot systems (OS X & OS 9) for the less experienced users can definitely pull on a few strings and unravel that ball of yarn. SO, as mentioned...a quick review for those who don't search the forum for old topics...
Mac System with OS 9 Only (Not Dual Boot)1) Keep Boot Volume less than 200GB (I always use 190GB)
2) If using a Mechanical Drive (non-SSD) keep ALL volumes less than 200GB if you will be running Norton Speed disk or other OS 9 de-fragmenting apps, an alternative is to boot to OSX via CD/DVD and run an OS X de-fragment app on the OS 9 Volume as some here members do...I do NOT do this, so you cannot ask me the details
3) NEVER de-fragment SSD volumes as this will shorten the life of the SSD for no reason (all locations pull data at the same time, so reason to beat up the SSD)
4) If using an SSD or drive you are never going to de-frag, make all non-boot volumes as big as you want, but remember that OS 9 data recover tools may run out of RAM or error out of some huge volumes
Mac System with OS 9 & OS X (Dual Boot)1) Separate Hard Drives for OS X and OS 9 (if possible); this adds a little extra safety with the benefit of being able to run OS specific data recovery/partition recovery tools if something goes wrong and not "confuse" the app
2) Disable Spotlight (as mentioned)
3) Disable Time machine (as mentioned)
4) Copy files to and from other volumes in OS9 (this will prevent OS X from messing with long file names that show up like hieroglyphics in os9) and also...
While you can move files without issues from OSX to OS9 in OSX, occasionally the Linux-derived OSX permissions will trip the wrong flag in OS9 and lock the file down.
as mentioned