IO 相关指标

vmstat:


   Swap
       si: Amount of memory swapped in from disk (/s).  
       so: Amount of memory swapped to disk (/s). 

si: 每秒从交换区写到内存的大小
so: 每秒写入交换区的内存大小

iostat:

    tps
 Indicate  the number of transfers per second that were issued to the device. 

A transfer is an I/O request to the device. Multiple logical requests can be com-bined into a single I/O request to the device. A transfer is of indeterminate size.


意思是每秒对设备的I/O请求数量。 多个逻辑的请求可以合并成一个I/O请求。
因为I/O一般是系统瓶颈。所以越大并不是越好。


sar:

              await
     The average time (in milliseconds) for I/O requests issued to the device to be served. This includes the time spent by the requests  in  queue  and  the  time
                     spent servicing them.

? await表示平均每次设备I/O操作的等待时间（以毫秒为单位）。