It seems the disk 1 is kind of failing i guess. As it reduced copying/writting speed from 100+ mb down to 40-72Mbps
I tried the same file with disk 2 its copies above 93Mb/s till 110Mb/s
Initial setup was JBOD 2x 2tb wd red .
Now did a re-raid - vol-1 with 1.82tb and 298gb spanning.
As changing from JBOD to this took like 2hrs plus only for disk 1. As disk 2 done in less than 15 min.
But to my surprise the disk 1 stuck at 90% for almost 2 hrs and frequent timeout as well.