How to Track Down/Find Cause of Linux high disk iowait/wa -

How to Track Down/Find Cause of Linux high disk iowait/wa

top - 09:34:12 up 2 days, 20:57,  2 users,  load average: 1.83, 1.99, 2.03
Tasks:  59 total,   2 running,  57 sleeping,   0 stopped,   0 zombie
Cpu(s):  0.3%us,  0.0%sy,  0.0%ni,  0.0%id, 99.7%wa,  0.0%hi,  0.0%si,  0.0%st

That 99.7% wa is iowait, it means the server is waiting for a process to complete an IO operation or in plain English, there is a delay in reading and/or writing data to the hard drive.

Here are some ways to get an idea of what is going on (in RPM based Distros this package is called "sysstat") and contains the very helpful binary called "iostat".  There's another package I like called "dstat" that does a great job too.

Run iostat -d 5 (it refreshes the data every 5 seconds):

Device:            tps   Blk_read/s   Blk_wrtn/s   Blk_read   Blk_wrtn
sda1              2.07         5.27        28.66    1309570    7120384
sda2              0.00         0.03         0.04       7496       8832

Device:            tps   Blk_read/s   Blk_wrtn/s   Blk_read   Blk_wrtn
sda1             27.15         0.00       357.68          0       1792
sda2              0.00         0.00         0.00          0          0

What we're seeing is that the iowait must be caused primarily by blocks being written to /dev/sda1 which is mounted as / (my root filesystem).  So now we know the main cause is by an application constantly writing to the root partition, but we still don't know what process is directly responsible for this.

If you have a newer kernel it's often possible to view processes by io usage, you can test for this by running: cat /proc/self/io

If the file is not found then you don't have io stats enabled in your kernel.  Then you can check a suspected process by running cat /proc/13/io (replace the 13 with the PID you want to check).

read_bytes: 0
write_bytes: 0
cancelled_write_bytes: 0

 


  • MySQL Adding New Field to Existing Database Table
  • MySQL Cannot Update/Write to any database table solution
  • Centos How To Update to Glibc 2.14 Plus
  • php remove last letters of string
  • MySQL Maximum INT Size Truncation Issue/Warning
  • MySQL How To Add New Field Column To Existing Table
  • mysql how to reset passwords with a few commands
  • htaccess apache how deny/allow to block or allow by IP address
  • PHP geoip.so fatal error Solution
  • Syntax error on line 221 of /etc/httpd/conf/httpd.conf: Syntax error on line 6 of /etc/httpd/conf.d/php.conf: Cannot load /etc/httpd/modules/libphp5.so into server: /etc/httpd/modules/libphp5.so: cannot open shared object file: No such file or direct
  • GCC 5 on Centos 6 - How To Install
  • bash find line and replace howto
  • How To Create Apache htpasswd file
  • possible SYN flooding on ctid 42131, port 80. Sending cookies. - Solution
  • Linux last command show login by IP instead of hostname
  • Install Windows From a Linux TFTP Server instead of using WDS Solution
  • How To Secure Samba NMBD/SMBD to bind to a specific IP address
  • tftp: client does not accept options - solution if you are using UEFI PXEBoot disable it!
  • Linux how to view video card make and exact model
  • Authentication refused: bad ownership or modes for directory /home/user SSH Public Key Authentication Failed Solution