Firstly -I am impressed with the new RAID6 and reshape features added recently - respect!
I am currently reshaping a RAID6 array from 6x1.5TB discs to 8x1.5TB discs. Simply - I have added 2 identical discs to an existing (almost empty) 6disc x RAID6 array. The operation started a 4 days ago and reporting running at 7000kb/s, and was consuming 5-6% CPU (load average 1.4-1.6 from memory). This was slower than I expected. (No raid controller, using 5x onboard SATA ports and 2x 2-port SIL SATA PCE-Express cards, Quad Core AMD 3GHz, 4GB RAM etc)
After 1-2 days I noted the rate of progress dropped very significantly, and "/proc/mdstat" now reports anything from 5000kbs to 200kbs, mostly around 500kbs. Everything was running OK but just miserably slow. After 4 days its now 71.2% complete.
I have just shutdown and restarted the machine and onreboot it has restarted the reshape and is currently running at a "proper" speed again at between 8000 and 10000 kbs (8-10MB/s). However, it may be after a few hours the rate drops back to 500kbs again?
Is this normal? What have I misconfigured?