For my personal reference (from http://jeff.blogs.ocjtech.us/2008/05/how-to-re-scan-scsi-bus-on-linux.html)
How to re-scan the SCSI bus on Linux:
echo “- – -” > /sys/class/scsi_host/host0/scan
Update: Tim Verhoeven has a more complete description of the re-scanning process.
http://misterd77.blogspot.com/2007/12/how-to-scan-scsi-bus-with-26-kernel.html