If you try to rescan the partition table of an active disk it will fail and require a reboot to discover new partitions.
You can get around this by using partx which will scan for individual new partitions and inject them into the running kernel.
#partx -v -a /dev/sda
root@linux # partx -l /dev/sda
# 1: 2048- 1026047 ( 1024000 sectors, 524 MB)
# 2: 1026048-1048575999 (1047549952 sectors, 536345 MB)
# 3: 1048576000-1572859889 (524283890 sectors, 268433 MB)
# 4: 0- -1 ( 0 sectors, 0 MB)
root@linux# partx -v -a /dev/sda
device /dev/sda: start 0 size 1572864000
gpt: 0 slices
dos: 4 slices
# 1: 2048- 1026047 ( 1024000 sectors, 524 MB)
# 2: 1026048-1048575999 (1047549952 sectors, 536345 MB)
# 3: 1048576000-1572859889 (524283890 sectors, 268433 MB)
# 4: 0- -1 ( 0 sectors, 0 MB)
BLKPG: Device or resource busy
error adding partition 1
BLKPG: Device or resource busy
error adding partition 2
added partition 3