设置监控哪块盘：
https://www.bountysource.com/issues/50160777-disk-space-usage-depcited-in-grafana-correct
https://www.google.com.hk/search?q=(sum(node_filesystem_size%7Bdevice!%3D%5C%22rootfs%5C%22%2Cinstance%3D%5C%22%24server%5C%22&oq=(sum(node_filesystem_size%7Bdevice!%3D%5C%22rootfs%5C%22%2Cinstance%3D%5C%22%24server%5C%22&aqs=chrome..69i57.567j0j7&sourceid=chrome&ie=UTF-8