Cody Yellan wrote:

quoted

I had a 4x500GB SATA2 array, md0.  I added one 500GB drive and
reshaping began at ~2500K/sec.  Changing
/proc/sys/dev/raid/speed_limit_m{in,ax} or
/sys/block/md0/md/sync_speed_m{in,ax} had no effect.  I shut down all
unnecessary services and the array is offline (not mounted).  I have
read that the throttling code is "fragile" (esp. with regard to
raid5) but does this make sense?  I will wait (in)patiently for it to
finish, but I do wonder why the configuration parameters have no
effect.  This is a dual quad 2GHz Xeon machine with 8GB of memory
running RHEL5.  Is this the maximum speed?

Are you running a non-standard /sys/block/md5/md/stripe_cache_size?

I found when running a kernel of about that vintage on FC6 (which I 
guess became RHEL5), that with a stripe_cache_size of 16384, resyncs 
dropped down to about the speed you are seeing.

This changed back to more normal speeds with a later kernel, but I do 
not recall which.

Regards,

Richard