What is jbd2/dm-0-8 and why It is consuming all my I/O usage and causing I/O wait?

Is there anyway to disable this?

Bonnie++ results: http://pastebin.com/iQCWP1qp

$ sudo hdparm -t /dev/sda1

 Timing buffered disk reads: 108 MB in  3.02 seconds =  35.71 MB/sec
  • 1
    Replace the slow and possibly failing disks with faster disks. – Michael Hampton Jan 2 '13 at 16:11
  • Thanks, as you mentioned about slow disks I attached my bonnie++ results. Is this kind of a slow disk? – Super Mario Jan 2 '13 at 18:38
  • Sheesh, the three year old drive on my desktop is faster than that. – Michael Hampton Jan 2 '13 at 18:45
  • Oh, even the hdparm result (added to my question) is bad enough to cause this? – Super Mario Jan 2 '13 at 18:48
  • Some details on how I tracked down what jbd2 was doing when it kept showing up with high % in iotop for me : serverfault.com/a/801223/181704 – Iwan Aucamp Sep 5 '16 at 23:51

jbd is the "journaling block device". dm-0-08 indicates a device mapped by device mapper. It just indicates that you are doing IO and it is being flushed out to disk properly. It is not by itself a source of IO.

Here is vague advice based on the vagueness of the question: If you need less iowait time, your machine needs to do less work, work more efficiently, or have more io resources to do work with.

  • Thanks, I tweaked settings as much as I could but still no change. I also added my bonnie++ results. I hope that might help if it's because slow disks. – Super Mario Jan 2 '13 at 18:40

Was the filesystem recently created? Is there any process named ext4lazyinit?

Then just wait as it inits (prepares, formats) the filesystem.

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