对硬盘的自带监控能力
磁盘读延迟(ms): node_disk_read_time_seconds_total
磁盘写延迟(ms): node_disk_write_time_seconds_total
磁盘每秒读取速率: node_disk_reads_completed_total
磁盘每秒写入速率: node_disk_writes_completed_total
读时延：
rate(node_disk_read_time_seconds_total{instance="my-instance-name"}[1m]) /
rate(node_disk_reads_completed_total{instance="my-instance-name"}[1m])
写时延：
rate(node_disk_write_time_seconds_total{instance="my-instance-name"}[1m]) /
rate(node_disk_writes_completed_total{instance="my-instance-name"}[1m])