MDADM has now the ability to manage external meta-data RAID devices and for some devices such as Intel Matrix RAID it's now preferred over using the common DMRAID package. With the broader move towards MDADM for Linux RAID administrator, Ubuntu developers are looking to follow this movement and transition to MDADM by default.
MDADM supports all the standard RAID configurations (RAID 0/1/4/5/6/10) and works with both partitions and entire disks. MDADM also supports container, multi-path, faulty, and linear disk configurations as well.
For those exploring RAID on Linux or want to catch up on MDADM, see the developer blog or the Git repository. What's new today is that Ubuntu developers are hoping to switch to MDADM by default over DMRAID.
There's changes needed by the Ubuntu installer, initramfs changes, dmraid/imsm migration items to work through, and other issues to work through, but it's now on the agenda for Ubuntu and potentially to be changed in 14.04 LTS. More details on the MDADM Ubuntu plans can be found via this Ubuntu vUDS page.