On a test machine Iwas never able to access to a newly created 4th partiton. As we can see there are dev devices for everything but the 4th partition.
The normal "partprobe" or "kpartx" or kernel being told to rescan the block device didn't help (only a reboot did).
fdisk -l /dev/sda
Disk /dev/sda: 750.2 GB, 750156374016 bytes
255 heads, 63 sectors/track, 91201 cylinders
From the package "parted" you can use the command "partprobe" to re-read the partition table. I really hate rebooting, and that's what Iloved to hear about AHCI motherboards, that they allow hotswap so you don't have to reboot. But that's only as good as the OS, if the OS does not reload the partition table you won't be able to do anything with that new drive you attached without rebooting. Yes, even without re-reading the partiton table Linux will........