ScriptBits, Little Bits Of Code You Cannot Live Without

An easy way to identify what process is generating your IO Wait load is to enable block I/O debugging. This is done by setting /proc/sys/vm/block_dump to a non zero value like:

echo 1 > /proc/sys/vm/block_dump

This will cause messages like the following to start appearing in dmesg:

bash(6856): dirtied inode 19446664 (ld-2.5.so) on md1

Using the following one-liner will produce a summary output of the dmesg entries:

dmesg | egrep "READ|WRITE|dirtied" | egrep -o '([a-zA-Z]*)' | sort | uniq -c | sort -rn | head
    354 md
    324 export
    288 kjournald
     53 irqbalance
     45 pdflush
     14 portmap
     14 bash
     10 egrep
     10 crond
      8 ncftpput

Once you are finished you should disable block I/O debugging by setting /proc/sys/vm/block_dump to a zero value like:

echo 0 > /proc/sys/vm/block_dump

Here's a real quick and easy process to set up network interface bonding on your Fedora, CentOS or Redhat box.  It assumes that your kernel already supports bonding and that your distro supports master/slave notation in the network interface configs.  Recompiling the kernel and/or installing ifenslave is beyond the scope of this article

Create bond0

cat /etc/sysconfing/network-scripts/ifcfg-bond0

DEVICE=bond0
IPADDR=192.168.1.1
NETMASK=255.255.255.0
NETWORK=192.168.1.0
BROADCAST=192.168.1.255
ONBOOT=yes
BOOTPROTO=none
USERCTL=no

Make eth0 and eth1 slaves of bond0

cat /etc/sysconfig/network-scripts/ifcfg-eth0

DEVICE=eth0
USERCTL=no
ONBOOT=yes
MASTER=bond0
SLAVE=yes
BOOTPROTO=none

cat /etc/sysconfig/network-scripts/ifcfg-eth0

DEVICE=eth1
USERCTL=no
ONBOOT=yes
MASTER=bond0
SLAVE=yes
BOOTPROTO=no

Edit modprobe.conf

cat /etc/modprobe.conf

# bonding commands
alias bond0 bonding
options bond0 mode=1 miimon=100

In the above, mode=1 is for failover and miimon=100 is to monitor link every 100 ms.  You can use mode=0 for round-robin, miimon=100 should probably stay just like that.

Load bonding driver and restart network, or reboot your computer.

$ modprobe bonding; service network restart

or

$ reboot now

You now have bonding configured!