CentOS 7/Kernel 3.10 or 5.6
ES can get io_stats when using ext4 or xfs but btrfs is empty on same system envrioment.
here is /proc/diskstats:
grep sdb /proc/diskstats
8 16 sdb 586393003 109982 30391265392 2199288329 262632645 14809281 122797050312 689016458 0 60590581 2473033176 0 0 0 0
it seems read/write stats are no zero but es not display.