Recently I assembled a server with several 2Tb disks in Linux RAID. RAID resync reported by cat /proc/mdstat showed that resync will take about 9 hours! More than my working day! I started to look for a way to increase resync speed.
echo 60000 >/proc/sys/dev/raid/speed_limit_min
to increase minimum speed at which resync is in process. But, however, if the machine is under no load, this doesn’t lead to any serious speed improvements. But if you are doing something on server at the same time, this may really improve resync speed. The value (60000) is the resync speed you want to be given in kilobytes per second. If you max it out, Linux will try to use all the speed it can get from disks (so, no magic here 🙂 )
Don’t forget to change it back to 1000 when you are done or on next RAID resync your server will hang flooded by user queries concurring with RAID resync process.