Comment 39 for bug 607560

Same problem here.

Ubuntu 10.10 64 bit / 2.6.35-28-generic
Disk one, Seagate barracuda 500 gig - ext4 - sda3 on /
Disk two, Samsung spinpoint 500 gig - ext4 - sdb1 on /home

I tried booting into the recovery mode with the shell and networking.
After a few seconds nothing, no jdb2. No disk activity at all running iotop.

This is the only time jdb2 did not access the disks.

After this I followed these instructions and on my system it worked:
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We can confirm that our ext4 partition is running a journal with: (where X is the partition number, sda1,2,3,4 etc)

$sudo dumpe2fs /dev/sdaX | grep has_journal

Disabling journaling is rather easy, the only drag is that to make structural changes to a filesystem, the filesystem cannot be mounted with read/write privileges. So, run a live cd, open a terminal and enter:

$sudo tune2fs -O ^has_journal /dev/sdaX

And it's done. Now when you boot, the change will be noted and the disk will be checked for errors. When the system is finally up we can run this again to confirm that in fact ext4 is running without a journal.

$sudo dumpe2fs /dev/sdaX | grep has_journal

should now return nothing.

With this quick fix, no more constant IO peaks.
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The tune2fs man page has this entry about 'has_journal'.

-O [^]feature[,...]

Set or clear the indicated filesystem features (options) in the filesystem. More than one filesystem feature can be cleared or set by separating features with commas. Filesystem features prefixed with a caret character ('^') will be cleared in the filesystem's superblock; filesystem features without a prefix character or prefixed with a plus character ('+') will be added to the filesystem.

The following filesystem features can be set or cleared using tune2fs:

has_journal
Use a journal to ensure filesystem consistency even across unclean shutdowns. Setting the filesystem feature is equivalent to using the -j option.