Can not prevent firewall from starting on CentOS?

I have disabled iptables from starting at booting time using chkconfig. Upon checking the status,

sudo chkconfig iptables --list
iptables       0:off 1:off 2:off 3:off 4:off 5:off 6:off

However, after rebooting the host, iptables was not disabled. What's going on?

Well, in  my case, I have daemon libvirtd starts at booting time which depends on iptables, automatically creates iptables rules for each started qemu network. After disable it from start, iptables was disbaled too.

sudo chkconfig libvirtd off

if this is not the case for you, please do check the content of /etc/rc.local file, to look for any active firewall rule, such as
/sbin/iptables -I INPUT -m iprange --src-range 10.208.42.196-10.255.255.255 -j DROP

and disbable it. Some other things to look at are, init script, cron jobs.
As a quick hack until it is solved, you could run echo "service iptables stop" >> /etc/rc.local

Dell H310 RAID Controller

My workstation running CentOS 6.7 hangups unexpected recently every since I re-imaged it. A little improvement has been seen by adding "elevator=noop" to the boot parameter. But it does not fix the source of the problem.
I has always been suspecting the raid controller, Dell H310. First I tried updating the firmware without any improvement. To update firmware in Linux, you could use Rufus (http://rufus.akeo.ie) to create a FreeDOS bootable USB driver and put the windows version of the firmware to the USB driver.
All these fixes did not eliminate the problem from source, I wrote an email to Dell support. Finally, I got confirmed from Dell tech support that "....While the controller can do RAID 5, we in tech support really only recommend RAID 0 or RAID 1 with that controller....."
After changing to RAID 0 and running a month now, I have never encountered the hangup again.