Back in the days of 100Mb disks, I had to do ugly things with symbolic links to run multiple copies
of SDE from a single SDEHOME (faking multiple SDEHOMEs to save disk space).
Now that ArcSDE supports multiple Oracle instances fom a single SDEHOME, I wouldn't consider
using that feature if I was running under 15-20 instances. Instead I copy the ora*exe directory
to D:\ESRI with the instance in the folder name (e.g. D:\ESRI\sdeexe931sp1_prod), open a
command window, set the SDEHOME and PATH to use %SDEOME%\bin, establish the correct
ORACLE_SID/LOCAL, and run 'sdeservice' manually. This way, when it's time to upgrade, I can
apply the SP to the base install without corrupting my instances, and upgrade them each over
time. The way I see it, the space savings on a 200-500Gb disk just aren't worth the dependencies
caused by using a single SDEHOME for multiple instances.
- V