On Wed, 13 Apr 2011 14:10:46 -0700 Rory Jaffe [off-list ref] wrote:

I have a RAID5 array with 4 active devices and two spares. The spares
are normally in sleep mode. I ran a resync with:

echo repair > /sys/devices/virtual/block/md0/md/sync_action

About 20 times (evenly spaced apart) during the resync, the spares
were written to, waking them up. Is that behavior desired? It seems to
me that it's a waste--I don't know why the resync would bother with
the spares.

Yes, there is room for optimisation there.  It really shouldn't write to
those devices.  I guess I should try (again) to fix that.

Thanks for the report.

NeilBrown