Tipps I found with variable usefullness:

blockdev --rereadpt /dev/sda7

(from VMWare Communities)

partprobe /dev/sdX

hdparm -z /dev/sda

sfdisk -R /dev/sda

echo 1 > /sys/block/sdX/device/rescan

echo "scsi remove-single-device X X X X" > /proc/scsi/scsi
echo "scsi add-single-device X X X X"    > /proc/scsi/scsi

(X X X X is <AdapterNo.> <Channel> <Id> <LUN>)

echo "- - -" > /sys/class/scsi_host/host<N>/scan

(see Linux Journal)

echo "scsi scsi-scan-devices" > /proc/scsi/scsi

partprobe [options]

(Thanks to linux-poweredge)

sfdisk -R