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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!), but nothing. Problem persists.

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migrated from Oct 15 '10 at 9:59

This question came from our site for professional and enthusiast programmers.

try - this is not a programming question – sje397 Oct 15 '10 at 6:15
This seems like more a system administration question than a programming one, so you're probably better off asking on My first instinct is to check dmesg for seek errors after this happens, but I could be way off. – Jander Oct 15 '10 at 6:20
Perhaps it's more of an AskUbuntu question? – schot Oct 15 '10 at 6:22
up vote 1 down vote accepted

Unfortunately, this is a problem with the disk itself. The WD Caviar Green disks have been causing this problem in a lot of places.

The problem stems from the 4k sector size being used. Apparently there's a jumper for 512b compatibility mode, but I've heard that doesn't help under Linux.

The good news is that you can RMA the drive, whereupon they will send you one that works properly. Still, WD don't seem to have handled this whole issue well at all.


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Yepp, seems you were right. Thanks for the help. – netom Mar 5 '12 at 8:28

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