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.