RAID1 over RAID0 misbehavior

I recently created a RAID1 mirror from two identical RAID0 arrays
under Linux 2.6.0.  I was surprised when /proc/mdstat reported a
resync speed of 1 MB/s, even though the system was otherwise idle.  I
increased the min sync rate in /proc/sys/dev/raid/speed_limit_min to a
large value, and was happy to see the resync rate increase to 40 MB/s.
It seems to me like something confused the RAID1 layer into thinking
there was lots of IO going on in the system.  My guess is that the
disk IO generated by the RAID0 is being overlooked by RAID1 as being
caused by the resync rather than other system activity.  Whatever the
cause, the current behavior is no good.  I have no idea how to fix it,
though.

-- 
Måns Rullgård
mru@kth.se

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