kernel upgrade giving high disk utilization

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yoor699
Posts: 3
Joined: 2019/01/09 15:21:11

kernel upgrade giving high disk utilization

Post by yoor699 » 2019/01/09 15:28:53

hi,

After last kernel upgrade on several cPanel servers using NVMe SSD, we get a high disk utilization according to iostat output, confirmed also by dstat -cd --disk-util (in case iostat would have a caveat : https://brooker.co.za/blog/2014/07/04/iostat-pct.html)

uname -a
3.10.0-957.1.3.el7.x86_64 #1 SMP Thu Nov 29 14:49:43 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux

Initial investigation :
- hardware is in perfect state in all servers, they use NVMe SSD for ages.
- such high level of disk utilization has no justification in term of running processes from any user, or any scripts, no iowait also at all
- what is reported by linux may be wrong, but this lets us a visible symptom that we can't trust, neither ignoring it util we have a realiable explanation.

we observed that :
- an upgrade centos on a basic server (with mechanic hdd in this case) is not causing this at reboot the following
- an excessive update of file /.readahead, this is not happening on other cpanel server using cloudlinux by ie
(our servers use no hard raid card)

We tried to disable readahead and reboot in case, but no change at all :
systemctl disable systemd-readahead-collect.service
systemctl disable systemd-readahead-replay.service

We contacted cPanel support, investigated deeply with 2 sysadmin, it appears that the answer will only come from centos 7 kernel developer

Thanks for your attention,
John

yoor699
Posts: 3
Joined: 2019/01/09 15:21:11

Re: kernel upgrade giving high disk utilization

Post by yoor699 » 2019/01/19 09:55:28

I now upgraded to latest centos 7

uname -a
Linux rep4.hosting1976.fr 3.10.0-957.1.3.el7.x86_64 #1 SMP Thu Nov 29 14:49:43 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux

Issue is still there, does someone has an explanation ?

hunter86_bg
Posts: 2019
Joined: 2015/02/17 15:14:33
Location: Bulgaria
Contact:

Re: kernel upgrade giving high disk utilization

Post by hunter86_bg » 2019/01/19 20:42:07

Open a bug in bugs.centos.org and then open another bug on bugzilla.redhat.com and relate that bug to the centos counterpart.

yoor699
Posts: 3
Joined: 2019/01/09 15:21:11

Re: kernel upgrade giving high disk utilization

Post by yoor699 » 2019/01/20 06:05:47


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