RAID5 scrub 1 or 2 disks at a time instead to speed up

[DanglingPointer <danglingpointerexception@xxxxxxxxx>]

Hi All,

I continually get frustrated each time I have a scrub a btrfs RAID5 
array due to the slow rate.
I was wondering if anyone has tried or seriously considered scrubbing 1 
or 2 disks at a time, instead of all disks engaged at the same time 
(perhaps a division check on number of disks before start) to see if it 
is indeed faster?

Zygo Blaxell mentioned the above idea on Feb 6 this year.  Just 
wondering if there's been any serious thought put into the merits of 
that idea?

The array I'm running the scrub on now has 7 disks (5x 2TB and 2x 6TB).  
If it is a question of diminishing returns on speed as the number of 
disks increases; perhaps we say up to 8 disks then do 1 or 2 at a time 
sequentially, then over 8 just do default like right now?

If it is indeed faster then it would make the uptake of btrfs RAID56 a 
lot more friendlier and decrease the amount of flak it gets in the wild.