Plesk interface very slow

[EricVis]

Plesk server with 20 websites, over a year on 11.0.9 Update #62, CentOS 2.6.32-431.23.3.el6.x86_64, intel i5 - no big issues, no high traffic webistes, load usually less than 0.5

Issues started suddenly one day, I noticed that plesk interface started to work very very slow and it generates load as high as 2.0 just to log in and browse thru subscriptions. Creating new subscription takes 2-3 minutes and load up to 3. Lots of I/O operations done by journaling which I haven't noticed past year. When run "top" command it shows %wa always above 5, sometimes up to 80%!!! Processes are witing for because high I/O. Journaling has been disable on var/www partition and my next step is to disabled it for system partition as well. Not sure if I'm going into right directions but I noticed jbd process (jopurnaling) taking lots of resources.
The problem is with entire server, very few http requests can generate load up to 3-4 easily. Slowness affects mostly Plesk, client websites seem to load fine but longer operations (timeconsuming php processes) can also cause high load and timeouts. We haven't touched the code and it worked great before.

Something changed and it caused I/O issue.
Anyone had similar issues?

 

[IgorG]

Have you tried to troubleshoot it with help of OS and Plesk logs investigaton?

 

[EricVis]

I have investigated all possible logs and haven;t found anything unusual.

The only thing that comes to my mind is kernel and some system packages update a while ago, possibly around that time when I noticed this issue but I can;t tell for sure.
It simply looks like php+mysql operations take a way longer that it used to, especially more complicated or longer running php processes

here is result of iotop command (atatched)