I have about 16 websites in a CentOS dedicated, and I am having some problems on high traffic hours, it seems to be a high disk I/O activity causing a general slowdown.
I've installed atop and this is what I see on the bottom (the server has been restarted thats why the values are so low):
*** system and process activity since boot ***
PID RDDSK WRDSK WCANCL DSK CMD 1/18
2176 1.7G 7.3G 854.4M 39 mysqld
671 1248K 3.0G 0K 13 flush-8:0
566 0K 1.1G 0K 5 jbd2/sda2-8
2401 124.2M 529.1M 22408K 3 crond
2032 2.2G 502.0M 0K 12 nginx
2360 425.8M 115.3M 4188K 2 httpd
flush-8:0 and jbd2/sda2-8 are the processes I see with iotop using 99% on the IO> column, and they are the processes that write the most on the hdd (after mysql). From what I saw in google this could be caused by some ext4 related bug, the current kernel is:
Linux srvr.com 2.6.32-71.29.1.el6.x86_64 #1 SMP Mon Jun 27 19:49:27
BST 2011 x86_64 x86_64 x86_64 GNU/Linux
I asked the hosting support to update the kernel and they tried but they now say that the server wont boot with the new installed kernel and they had to go back to the previous, they are not helping very much.
Does someone has any idea how could I solve the high disk usage caused by flush-8:0 and jbd2/sda2-8 processes?
Best Answer
You haven't given us enough info for me to tell, but my first hunch would be that you are overusing RAM, and churning swap. with atop, show us the memory listing (press m), including the header section.
Don't blame your support. Your kernel and ext4 are very unlikely to be the problem.