【Device Utilization Report】
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 combined into a single I/O request to the device. A transfer is of indeterminate size.
Blk_read/s --(kB_read/s, MB_read/s) Indicate the amount of data read from the device expressed in a number of blocks (kilobytes, megabytes) per second. Blocks are equivalent to sectors and therefore have a size of 512 bytes.
Blk_wrtn/s --(kB_wrtn/s, MB_wrtn/s) Indicate the amount of data written to the device expressed in a number of blocks (kilobytes, megabytes) per second.
Blk_read --(kB_read, MB_read) The total number of blocks (kilobytes, megabytes) read.
Blk_wrtn --(kB_wrtn, MB_wrtn) The total number of blocks (kilobytes, megabytes) written.
rrqm/s --The number of read requests merged per second that were queued to the device. 每秒合并的读请求数（使用-x参数时出现此统计，下同）。
wrqm/s --The number of write requests merged per second that were queued to the device. 每秒合并的写请求数。
r/s --The number (after merges) of read requests completed per second for the device. 系统每秒发出的读请求数。
w/s --The number (after merges) of write requests completed per second for the device.系统每秒发出的写请求数。
rsec/s --(rkB/s, rMB/s) The number of sectors (kilobytes, megabytes) read from the device per second. 系统每秒的读数据量(单位为扇区，512字节)。
wsec/s --(wkB/s, wMB/s) The number of sectors (kilobytes, megabytes) written to the device per second. 系统每秒的写数据量（单位为扇区，512字节)。
avgrq-sz --The average size (in sectors) of the requests that were issued to the device. 系统平均每个读请求大小(单位为KB)。
avgqu-sz --The average queue length of the requests that were issued to the device. 统平均每个写请求大小(单位为KB)。
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. 系统平均每个I/O请求的wait时间（从放入队列到I/O完成）。
r_await --The average time (in milliseconds) for read requests issued to the device to be served. This includes the time spent by the requests in queue and the time spent servicing them.
w_await --The average time (in milliseconds) for write requests issued to the device to be served. This includes the time spent by the requests in queue and the time spent servicing them.
%util --Percentage of CPU time during which I/O requests were issued to the device (bandwidth utilization for the device). Device saturation occurs when this value is close to 100%. I/O的使用率，也就是I/O请求队列中有请求的时间占所有时间的百分比。
一般而言：
>. util值为100%左右表明系统的I/O非常忙，磁头基本上没有空闲的时间。
>. 对RAID卡而言，在随机读写比较多的情况下，（r/s + w/s）大概在1000左右的时候，I/O基本上就处于极限了。
