This normally works the other way around.
RAID is an acronym for Redundant Array of Independant Disks, and with it you can create large "md" devices across multiple physical devices (or partitions upon those devices) of the same size. Attempting to RAID mis-sized drives results in the RAID capacity being reduced.
There are many types of RAID, from level 0 (no parity, no loss of storage), 1 ("mirroring" - two devices only, exact duplication, halved capacity) and levels beyond those such as 5 and 6 (parity distributed across all drives, storage reductions as an equation of how many devices there are). It is a complex system and to fully explain it is beyond the scope of this site.
Logical Volume Management is a means of creating logical volumes within the partition space of one or many physical devices. It provides a great degree of flexibility over traditional partitions by being easier to resize the logical volumes "on-the-fly", and it's possible to create LV's on top of a RAID array, which you cannot partition traditionally.
This is the way it is usually done, with LVM on top of RAID.