Very often when you are busy with VMWare, you need an extra disk. Now creating the disk can happen while the VM Linux guest is active. However you don't see the disk immediately. A reboot will help obviously, but I found a nice script on http://www.garloff.de/kurt/linux/ that will show the new SCSI device, so that you can continue and add the disk without a reboot. Just search for the rescan-scsi-bus.sh script.
It is on my VMWare Server now and will go directly to each new Linux guest from now on. Any possibility to prevent a reboot is welcome ;-)