On Mon, 08 Feb 2016 18:22:34 +0900
Tomasz Chmielewski <tch@virtall.com> wrote:

> Linux 4.4.0 - btrfs is mainly used to host lots of test containers, 
> often snapshots, and at times, there is heavy IO in many of them for 
> extended periods of time. btrfs is on HDDs.
> 
> 
> Every few days I'm getting "no space left" in a container running mongo 
> 3.2.1 database. Interestingly, haven't seen this issue in containers 
> with MySQL. All databases have chattr +C set on their directories.

Hello,

Do you snapshot the parent subvolume which holds the databases? Can you
correlate that perhaps ENOSPC occurs at the time of snapshotting? If yes, then
you should try the patch https://patchwork.kernel.org/patch/7967161/

(Too bad this was not included into 4.4.1.)

-- 
With respect,
Roman