[ChuckMcM]

Having worked at NetApp for a few years at the turn of the century this is "old" news :-) But it is always important to internalize this stuff. M3 (or 3x mirrors) is still computationally the most efficient (no compute just I/O to three drives), R6 is the most space efficient at the expense of some CPU. Erasure codes are great for read only data sets (they can be relatively cheap and achieve good bandwidth) but they suffer a fairly high I/O burden during write (n data + m code blocks for one read-modify-write).

Bottom line is that reliably storing data is more complicated than just writing it on to a disk.