Advantages of partitioning RAID HDs?

Partitioning a disk for MD RAID duties has some advatanges:

• MBR/GPT partition table serves as a protective layer if/when the disks are installed on a non-linux machine (a partition table is a strong indication the disk was in using in other systems and it may contain valuable data);

• using a slightly smaller partition (versus the entire disk size) ensure that you can replace one failed disk with another 3 TB model even if the latter misses some sectors (ie: it is slightly smaller than the original disk);

• you can dedicate some partitions to a different RAID layout based on the expected data (for example, using RAID0 for swap and scratch data).

For simplicitly sake, if not booting off the RAID array and not needing a swap partition on it, I would probably not use partition for the MD array. This is especially true when using RAID inside a virtual machines, where the underlying disk can be resized by the hypervisor (requiring you to resize the partition table before growing the array).

On the other hands, for a bare metal installation, using a partition table for a RAID array only commands an extremely small overhead/annoyance, so if any of the above points is significant for you, go ahead with partitioning.