Comment 7 for bug 1649872

I'm unable to reproduce this on s390x either; steps I took to reproduce:

Bootstrap local LXD provider using ZFS backend.

juju deploy -n 3 ceph-mon
juju deploy -n 3 ceph-osd && juju config ceph-osd osd-devices=/srv/osd use-direct-io=False
juju deploy ceph-fs
juju add-relation ceph-mon ceph-osd
juju add-relation ceph-mon ceph-fs

I then mounted the cephfs created from the host system:

sudo mount -t ceph 10.189.59.86:6789:/ /mnt/cephfs -o name=admin,secret=AQDW91xZWcFvIhAAbWVm3x6xx1LBDgvW7RyP9g==

after which I was able to write files to /mnt/cephfs:

ubuntu@s4lpb:/mnt/cephfs$ ls -lrt
total 314880
-rw-r--r-- 1 root root 322437120 Jul 3 21:54 zesty-server-cloudimg-arm64.img
-rw-r--r-- 1 root root 0 Jul 5 10:36 a
-rw-r--r-- 1 root root 0 Jul 5 10:36 b

ubuntu@s4lpb:/mnt/cephfs$ df -h
Filesystem Size Used Avail Use% Mounted on
[...]
10.189.59.86:6789:/ 43G 6.1G 37G 15% /mnt/cephfs

Confirming kernel version:

$ uname -a
Linux s4lpb 4.4.0-67-generic #88-Ubuntu SMP Wed Mar 8 16:39:07 UTC 2017 s390x s390x s390x GNU/Linux
ubuntu@s4lpb:/mnt/cephfs$