I'm using Ubuntu, and I've got the same problem with Lucid and Maverick.

From time to time, especially a few minutes after boot, the iowait goes between 50-100% and the box is unusable. Everything that tries to access the disk freezes.

I have the following setup:

Hard disk:

Model Family:     Western Digital Caviar Green family
Device Model:     WDC WD15EADS-00P8B0
Serial Number:    WD-WMAVU0391287
Firmware Version: 01.00A01
User Capacity:    1.500.301.910.016 bytes

I have a quad core Intel Core2 Q6600 processor, and 4G of memory.

When the high iowait occurs, usually 4 processes are active:

• kdmflush (two procs)
• jbd2/dm-0-8
• jbd2/db-1-8

and a few more starving user processes of course.

I know this from top and iotop.

Any suggestions about why this is happening?

There are a lot of q/a-s about linux and high iowait, but none of them helped so far, I even tweaked the hard disk not to park the head in every 8 seconds (Load cycle count is 50334!!!!! :o ), but nothing. Problem persists.

Thank you in advance.