Hotadd CPU/Memory corrupts sar data file

Solution In Progress - Updated -

Environment

  • RHEL6
  • RHEL7
  • Virtual machines

Issue

  • RHEL6 after hot plugging cpu/memory the sar files become invalid.
# sar
Invalid system activity file: /var/log/sa/sadd
  • RHEL7 sar file is missing earlier sar data before hotadd cpu/memory.

Resolution

  • RHEL6
- This is a known issue and cannot be fixed in RHEL6's sysstat version as the patch may cause compatibility issue.
- The workaround would be to take a backup of the current date's "saxx" file before hotadding.
  • RHEL7
- In RHEL7 the sa does not gets corrupted or invalid. However the file loses all previous data before the hotplug activity.
- Similar workaround take backup of existing 'sa' file before hotadding.

Root Cause

  • RHEL6/7 does not have the complete hot-add support patches.

Diagnostic Steps

  • RHEL6
# sar
Invalid system activity file: /var/log/sa/sadd
  • RHEL7 sar data prior to hot-add is not available.
# journalctl -k | grep -i hot
Feb 13 16:54:26 hostname kernel: CPU4 has been hot-added
Feb 13 16:54:26 hostname kernel: Will online and init hotplugged CPU: 4
Feb 13 16:54:26 hostname kernel: CPU5 has been hot-added
Feb 13 16:54:26 hostname kernel: Will online and init hotplugged CPU: 5

# sar -u
Linux 3.10.0-957.1.3.el7.x86_64 (hostname) 02/13/2019   _x86_64_    (6 CPU)

05:00:01 PM     CPU     %user     %nice   %system   %iowait    %steal     %idle
05:10:01 PM     all      0.20      0.00      0.14      0.00      0.00     99.66
Average:        all      0.20      0.00      0.14      0.00      0.00     99.66

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