Redhat Linux: how to add/remove hard disk without rebooting server

A few years ago, I managed a few hundred of Redhat Linux servers, most of them are DELL PowerEdge 1750, 1850, and 1950.
Sometimes I needed to move the harddisk between servers. Removing or adding hardisks normally requires system reboot.
But I used this way to remove or add disk without rebooting:

echo 'scsi remove-single-device 0 0 1 0' > /proc/scsi/scsi
echo 'scsi add-single-device 0 0 1 0' > /proc/scsi/scsi

Recently I was asked to add a new harddisk without reboot system. It's a Redhat in VMware, as I was not managing VMware, so not clear about the hostadaptor, SCSI channel, ID, LUN, manipulating /proc/scsi/scsi may not work.

After searching around I found that I can let system to rescan the SCSI bus.

for scsi_host in /sys/class/scsi_host/host*
do
    echo '- - -' > $scsi_host/scan
done

After this, I could see the new hard disk was spinned up in /var/log/message.

Besides 'scsi remove-single-device 0 0 1 0', we can also do it in this way to remove a hard disk.

echo 1 > /sys/block/sdb/device/delete

Reference:
http://www.tldp.org/HOWTO/archived/SCSI-Programming-HOWTO/SCSI-Programming-HOWTO-4.html
http://www.cyberciti.biz/tips/vmware-add-a-new-hard-disk-without-rebooting-guest.html