AFAIK the snapshots are useful when the journal sits inside the OSD filesystem. In case the journal is on a separate filesystem/device then OSD BTRFS snapshots can be safely disabled. I have done so on my OSDs as they all use external journals and experienced a reduction in periodic writes, but they are not completely gone.
pon., 22.06.2015 o 11:27 użytkownik Jan Schermer <jan@xxxxxxxxxxx> napisał:
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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