Using linux-2.0.37-raid0145-19990724 and raidtools-0.90-19990421, I ran across a problem where I tried to add a partition into a degraded-mode raid5 array and managed to freeze up the sync process. What happened was that I was trying to raidhotadd /dev/md4 /dev/sde9 while the sde9 device node did not exist (I didn't catch this at first because sd[abcd]9 did), and somehow the raid subsystem decided what I was trying was adding /dev/md4 to itself! Couldn't catch the kernel debug messages from the raid code since the system was effectively hung (I think it was responding to some things, but I was running in single-user mode and couldn't regain control of the console), but this should be fairly repeatable. Fortunately, no data loss was caused by this. -- Osma Ahvenlampi
