Re: Unexpected disk write activity with btrfs OSDs

Burkhard Linke <Burkhard.Linke@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> · Fri, 19 Jun 2015 09:06:33 +0200

I don’t run Ceph on btrfs, but isn’t this related to the btrfs snapshotting feature ceph uses to ensure a consistent journal?
Jan

On 19 Jun 2015, at 14:26, Lionel Bouton <lionel+ceph@xxxxxxxxxxx> wrote:

    On 06/19/15 13:42, Burkhard Linke
      wrote:

      Forget the reply to the list...

        -------- Forwarded Message --------

              Subject:

              Re:  Unexpected disk write activity with
                btrfs OSDs

              Date:

              Fri, 19 Jun 2015 09:06:33 +0200

              From:

              Burkhard Linke <Burkhard.Linke@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx>

              To: 
              Lionel Bouton <lionel+ceph@xxxxxxxxxxx>

        Hi,

On 06/18/2015 11:28 PM, Lionel Bouton wrote:
> Hi,
*snipsnap*

> - Disks with btrfs OSD have a spike of activity every 30s (2 intervals
> of 10s with nearly 0 activity, one interval with a total amount of
> writes of ~120MB). The averages are : 4MB/s, 100 IO/s.

Just a guess:

btrfs has a commit interval which defaults to 30 seconds.

You can verify this by changing the interval with the commit=XYZ mount 
option.

    I know and I tested commit intervals of 60 and 120 seconds without
    any change. As this is directly linked to filestore max sync
    interval I didn't report this test result.

    Best regards,

    Lionel

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