Approximately twice a week, the entire graphical interface will lock up for about 10-20 seconds without warning while I am doing simple tasks such as browsing the web or writing a paper. When this happens, GUI elements do not respond to mouse or keyboard input, and the System Monitor applet displays 100% IOWait processor usage.

Today, I finally happened to have GNOME Terminal already open when the problem started. Despite other applications such as Google Chrome, Firefox, GNOME Do, and GNOME Panel being unresponsive, the terminal was usable. I ran iotop and observed that commands named [flush-8:16] and [jbd2/sdb2-8] were alternately using 99.99% IO.

What are these, and how can I prevent them from causing GUI unresponsiveness?

Details

$ mount | grep ^/dev
/dev/sda1 on / type ext4 (rw,noatime,discard,errors=remount-ro,commit=0)
/dev/sdb2 on /home type ext4 (rw,commit=0)

/dev/sda is an OCZ-VERTEX2 and /dev/sdb is a WD10EARS. Here is dumpe2fs /dev/sdb2, if it's relevant.