Linux 服务器高I/O 等待延迟问题查找

0. 首先是top查看一下系统状况

发现两个参数异常，一是平均负载高，一是cpu %wa一直在50%以上。

查了一下%wa参数的意义：

wa -- iowait
 Amount of time the CPU has been waiting for I/O to complete.

1. 查看磁盘读写数据

用iostat 查看磁盘状况

$ iostat -x 2 5
 avg-cpu: %user %nice %system %iowait %steal %idle
  3.66 0.00 47.64 48.69 0.00 0.00

 Device: rrqm/s wrqm/s r/s w/s rkB/s wkB/s avgrq-sz avgqu-sz await r_await w_await svctm %util
 sda 44.50 39.27 117.28 29.32 11220.94 13126.70 332.17 65.77 462.79 9.80 2274.71 7.60 111.41
 dm-0 0.00 0.00 83.25 9.95 10515.18 4295.29 317.84 57.01 648.54 16.73 5935.79 11.48 107.02
 dm-1 0.00 0.00 57.07 40.84 228.27 163.35 8.00 93.84 979.61 13.94 2329.08 10.93 107.02

2.查看进程状态

进程状态表

PROCESS STATE CODES
 D uninterruptible sleep (usually IO)
 R running or runnable (on run queue)
 S interruptible sleep (waiting for an event to complete)
 T stopped, either by a job control signal or because it is being traced.
 W paging (not valid since the 2.6.xx kernel)
 X dead (should never be seen)
 Z defunct ("zombie") process, terminated but not reaped by its parent.

查看到进程中状态D（disk sleep）的进程

# for x in `seq 1 1 10`; do ps -eo state,pid,cmd | grep "^D"; echo "----"; sleep 5; done

查看到有kjournald这个进程

查看这个进程是做什么的？

kjournald是ext3文件系统记录文件系统日志的进程。

查看进程相关状态信息

# cat /proc/487/io
 rchar: 48752567
 wchar: 549961789
 syscr: 5967
 syscw: 67138
 read_bytes: 49020928
 write_bytes: 549961728
 cancelled_write_bytes: 0

查看都往哪写东西了

# lsof -p 487

引起kjournald 状态D的原因还在查。。。。