When adding a new disk to a live system (e.g. a linux VM), the new disk may not always show up. Additionally, when resizing a disk through the hypervisor, the VM may not always immediately have the new size available for use. Luckily, you can trigger a rescan of the SCSI bus through the sysfs system.

For this to work, you'll need to have shell and root access to the server/VM.

Modern linux kernels automatically detect the addition of a disk, but in case it doesn't, you can trigger a rescan of a specific (virtual) SCSI controller:

echo "- - -" > /sys/class/scsi_host/hostX/scan

Replace hostX with the number of the SCSI controller, where host0 is the first, host1 is the second, et  ...