If you are running Linux, then you can use LVM (Logical Volume Manager) to get an extra flexibility in the way you allocate your disk space.
Physical disks are wrapped in Physical Volumes (PVs), which are grouped in Volume Groups (VGs). Logical Volumes (LVs) can then be laid over a VG.
So, if you want do manage a disk through LVM, you start by creating a PV for it ( with pvcreate ).
Once this is done, the disk is ready to be used in LVM. You can then choose either to create a VG for this disk alone (with vgcreate), or to add it to an existing VG (with vgextend).
The added space of this disk is now available to be used in the LVs which are laid over this VG either by creating a new LV (with lvcreate) or extending an existing LV (lvextend).
If you decide to extend an existing LV, you’ll probably have to extend the filesystem (i.e : ext2fs, ext3fs, reiserfs …) too with the appropriate command (maybe resize2fs or resize_reiserfs).
References : LVM How-To
Man pages for lvm and related pages