I've a nagios server which was perfectly working up to a few days ago. I've stopped it and restarted it to increase its RAM, and since then, iowait increased dramatically on the server (more than 20%, it was less than 1% before). I've tried to put back the original amount of RAM on the server but I still get the same issue.

I've readed lots of similar iowait problems on serverfault, but I never manage to find the explaination in my case :

Looking at iotop, I see there is a lot of io for pdflush, which is doing page cache & kjournald, which is dedicated for journaling ext3 filesystem. I don't know if it's normal. According to other serverfault questions, i've tried to put noatime in fstab. Ext3 filesystem is mounted with ordered data mode

```
Total DISK READ: 0.00 B/s | Total DISK WRITE: 210.44 K/s
TID PRIO USER DISK READ DISK WRITE SWAPIN IO> COMMAND
650 be/3 root 0.00 B/s 0.00 B/s 0.00 % 99.99 % [kjournald]
11482 be/4 root 0.00 B/s 0.00 B/s 0.00 % 98.42 % [pdflush]
12167 be/4 nagios 0.00 B/s 0.00 B/s 0.00 % 0.12 % nagios -d /srv/eyesofnetwork/nagios-3.4.1/etc/nagios.cfg
11 rt/3 root 0.00 B/s 0.00 B/s 0.00 % 0.10 % [migration/3]
12168 be/4 nagios 0.00 B/s 0.00 B/s 0.02 % 0.08 % nagios -d /srv/eyesofnetwork/nagios-3.4.1/etc/nagios.cfg
12165 be/4 nagios 0.00 B/s 0.00 B/s 98.42 % 0.02 % nagios -d /srv/eyesofnetwork/nagios-3.4.1/etc/nagios.cfg
2600 be/3 root 0.00 B/s 0.00 B/s 0.00 % 0.02 % auditd
12164 be/4 nagios 0.00 B/s 0.00 B/s 0.00 % 0.00 % nagios -d /srv/eyesofnetwork/nagios-3.4.1/etc/nagios.cfg
8 rt/3 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % [migration/2]
20 rt/3 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % [migration/6]
26 be/3 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % [events/0]
23 rt/3 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % [migration/7]
3047 be/4 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % snmpd -Ln -Lf /dev/null -p /var/run/snmpd.pid -a
12169 be/4 nagios 0.00 B/s 0.00 B/s 0.12 % 0.00 % nagios -d /srv/eyesofnetwork/nagios-3.4.1/etc/nagios.cfg
14 rt/3 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % [migration/4]
2601 be/3 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % auditd
5 rt/3 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % [migration/1]
17 rt/3 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % [migration/5]
5228 be/4 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % bash
10 rt/3 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % [watchdog/2]
13 rt/3 root 0.00 B/s 0.00 B/s 0.10 % 0.00 % [watchdog/3]
```

the following line

```
12165 be/4 nagios 0.00 B/s 0.00 B/s 98.42 % 0.02 % nagios -d /srv/eyesofnetwork/nagios-3.4.1/etc/nagios.cfg
```

seems quite surprizing : how can I have 98.42% of swapin since I have almost no swap :

```
free -o
total used free shared buffers cached
Mem: 4046468 3163796 882672 0 103548 2193604
Swap: 4192956 1572 4191384
```

top don't show something specific, exept high load and high iowait

```
top - 10:07:56 up 12 days, 23:42, 4 users, load average: 8.60, 9.29, 9.85
Tasks: 177 total, 1 running, 176 sleeping, 0 stopped, 0 zombie
Cpu(s): 0.1%us, 0.0%sy, 0.0%ni, 77.2%id, 22.6%wa, 0.0%hi, 0.0%si, 0.0%st
Mem: 4046468k total, 3165500k used, 880968k free, 104204k buffers
Swap: 4192956k total, 1572k used, 4191384k free, 2201500k cached
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
5246 root 15 0 14252 2632 836 R 0.3 0.1 0:03.94 top
1 root 15 0 10372 696 584 S 0.0 0.0 0:03.61 init
2 root RT -5 0 0 0 S 0.0 0.0 0:14.80 migration/0
3 root 34 19 0 0 0 S 0.0 0.0 0:00.73 ksoftirqd/0
4 root RT -5 0 0 0 S 0.0 0.0 0:00.00 watchdog/0
5 root RT -5 0 0 0 S 0.0 0.0 0:13.93 migration/1
6 root 34 19 0 0 0 S 0.0 0.0 0:01.75 ksoftirqd/1
7 root RT -5 0 0 0 S 0.0 0.0 0:00.00 watchdog/1
8 root RT -5 0 0 0 S 0.0 0.0 0:09.51 migration/2
9 root 34 19 0 0 0 S 0.0 0.0 0:01.09 ksoftirqd/2
10 root RT -5 0 0 0 S 0.0 0.0 0:00.00 watchdog/2
11 root RT -5 0 0 0 S 0.0 0.0 0:08.98 migration/3
12 root 34 19 0 0 0 S 0.0 0.0 0:01.46 ksoftirqd/3
13 root RT -5 0 0 0 S 0.0 0.0 0:00.00 watchdog/3
14 root RT -5 0 0 0 S 0.0 0.0 0:20.36 migration/4
15 root 34 19 0 0 0 S 0.0 0.0 0:01.15 ksoftirqd/4
16 root RT -5 0 0 0 S 0.0 0.0 0:00.00 watchdog/4
```

disabling nagios process make the system load normal (i.e. < 1 ) but i still get high iowait.

In atop, the DSK is 100% busy, even with no nagios process running. May I have a hard drive problem? (it's a western digital green, which is not supposed to be running in such a server). I get no special message on dmesg or syslog.