Getting high iowait on local disk on one system while comparing with the identical system

Solution Verified - Updated -

Environment

  • Red Hat Enterprise Linux 5
  • HP ProLiant DL380 G6

Issue

  • Getting high iowait on local disk on one system while comparing with the identical system
  • Running "dd" command to check the speed of the disk on the system has same hardware and firmware.

Resolution

  • Although the hardware and firmware are same, the local disk had different speed.
  • Difference in the "dd" output
[root@node1]#  time -p dd if=/dev/zero bs=8192 count=1048576 of=/local/test
1048576+0 records in
1048576+0 records out
8589934592 bytes (8.6 GB) copied, 97.5234 seconds, 88.1 MB/s
real 97.52
user 0.35
sys 9.70

[root@node2]#  time -p dd if=/dev/zero bs=8192 count=1048576 of=/local/test
1048576+0 records in
1048576+0 records out
8589934592 bytes (8.6 GB) copied, 40.9214 seconds, 210 MB/s
real 41.75
user 0.35
sys 9.47

Root Cause

  • The issue was due to missmatch speed of HD .

Diagnostic Steps

  • Gather sosreport
  • Output files from the following commands could be collected together as an archive file. The commands should be run when the system is facing issue.
[root@host]# top -n 5 -b > /tmp/top.out  
[root@host]# vmstat 1 50 > /tmp/vm.out  
[root@host]# iostat -x 2 10 > /tmp/io.out  
[root@host]# ps -aux > /tmp/ps.out  
[root@host]# sar 1 50 > /tmp/sar.out  
[root@host]# tar cjvf outputs.tar.bz2 \*out

This solution is part of Red Hat’s fast-track publication program, providing a huge library of solutions that Red Hat engineers have created while supporting our customers. To give you the knowledge you need the instant it becomes available, these articles may be presented in a raw and unedited form.

Comments