Why is this limitation set? We've been running webserver docroots under /w for decades without issues in debian. I was trying to make migrating domains easier and make ispconfig use /w as basedir path as well, alas, it fails..
Btw. Make a symlink for /w to /var/www to be able to access the directory in the same way you did before or use the website symlink settings field to add additional symlinks like /w/domain.tld => /var/www/clients/clientX/webX/web
