Quoting Andrew Greig (pushin.linux@gmail.com):
Thanks Rick, I travelled so long without problems that technology has oustripped my understanding. It is 18 years on Linux for me and around 17.5 since you informed me (graciously) about the bad habit of cross posting. So nice to hear from you.
Delighted to hear from you, too, Andrew. I should have added that, at least on all Linux system implementations I've seen for the past couple of decades, the mdadm.conf file ends up being slightly redundant during normal operation, because array construction stores all required RAID metadata for the RAID array in the RAID superblock stored on each physical device in the array. ISTR that mdadm.conf can be fully reconsructed from that stored metadata, even. That's talked about briefly, here: https://raid.wiki.kernel.org/index.php/RAID_setup#The_Persistent_Superblock_... The larger point I'm making is that md RAID has become, over a long period of time, pretty bulletproof, speaking in general terms. (Of course, nothing is entirely safe from an absent-minded sysadmin. ;-> )