Hi,
Shadow System resides inside SUM directory itself, So you have now:
/usr/sap/<sid>/SUM ------> SUM Directory
Space required for this : 20 GB (Base requirement) + Size of atleast "/usr/sap/<sid>" i.e. the Main instance for shadow.
As a rough estimation for SUM Directory, I take atleast 50 GB for SPS Updates and 80 GB for release upgrades.
Apart from this, All SP updates, Patches, DVDs that you need based on the upgrade goes into the download directory --- It is the size of your downloads from service marketplace itself so easy to see.
and /usr/sap/trans (DIR_TRANS) --- Atleast 20 GB free. (According to my experience make the free space more than the size of downloads. Guide mentions 20 GB as they have estimated the size of downloads the same too.
Warm Regards,
Ajay Kalra