I just wanted to publish my paper on RAID-X here so that it’s freely available to anyone interested. I’m currently working on this idea where you can have different sized disks in a RAID. Simply put, if you know about stripe units in RAID, I’m taking the stripe units and calling them chunks instead to get away from the common conception that stripe units in a stripe are at particular logical address on all the disks. Chunks in a particular stripe on the other hand can be anywhere on the disk. For this we need a small lookup table. Considering the fact that your cell phone has more RAM than a computer of the late 80s (when RAID was introduced), this lookup table is a small price to pay.
In addition, we now have dynamically resizable filesystems. RAIDX can take this into account. In traditional RAID, it is not possible to expand the storage capacity by adding additional disks. RAIDX does offer this feature. Going in the other direction, if a disk fails and the underlying filesystem can be resized to fit into the current smaller size, it is possible to become fully redundant once again with RAIDX.
Hope it helps someone, and if you have questions or comments, feel free to let me know.