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Doing: mdadm --stop /dev/md# Results in md# being removed from /proc/mdstat (as it should), but for some reason /sys/block/md# (and thus the /dev/md# created by udev) stick around. Monitoring udev events reveals that /sys/block/md# actually disappears, but at the very end seems to get recreated (by mdadm I assume) for some strange reason.
This bug appears to have been reported against 'rawhide' during the Fedora 12 development cycle. Changing version to '12'. More information and reason for this action is here: http://fedoraproject.org/wiki/BugZappers/HouseKeeping
This doesn't appear to be related to mdadm in any way. An strace of mdadm shows that it has nothing to do with the recreate events that the kernel issues to udev. I suspect that when they attempted to change the kernel to completely remove stopped devices, that either race conditions or user space breakages were encountered, so now the kernel stops the active array and recreates a new, blank array place holder. As such I'm closing this as WONTFIX (partially because regardless of whether or not it's fixed, mdadm isn't the culprit, and partially because I suspect it really needs to be WONTFIX until upstream decides to fix it).