mdadm: speedup resync process

[Franco Martelli <martellif67@gmail.com>]

Hello,

I've a RAID5 array of 4 HDDs (3+1spare), my goal is to speedup mdadm's 
resyncing process, sometime after a (rare) system freeze mdadm starts a 
resync process, just after the reboot, and it takes 1½ hour to complete 
the process.

It seems to me that mdadm uses a single core during the resync process, 
is it possible to configure mdadm to use all the core of my CPU for the 
resync?

Is it safe and the right thing to do increase the value of: 
"stripe_cache_size"? The default value is:

~# cat /sys/block/md0/md/stripe_cache_size
256

or play with "speed_limit_max" value, the default is:

~# cat /proc/sys/dev/raid/speed_limit_max
200000


Thanks in advance, kind regards.
--
Franco Martelli