* mdadm needs super-user privileges, but /proc/mdstat is readable for nobody
* fetch an array state from mdstat 'reshape|check|resync|recovery'
* reshape, recovery: rebuilding array -> set percent to _rebuild.value
* check, resync: data scrubbing or mirror rebuilding => set percent to _check.value
* resync=DELAYED|PENDING => set both to zero, because details are unknown even if using mdadm
* more info about /proc/mdstat => kernel src:/drivers/md/md.c, md_seq_show()
* one line regular expression matching to multiline text is a bit hard to picture
* apply regular expressions to each line
* first line should like "active raid1 sda1[0] sdc1[2] sdb1[1]"
* second line should like "123456 blocks super 1.2 [2/2] [UU]"
* third line will appear when the array is in action
