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** Changed in: linux (Ubuntu)
       Status: New => Incomplete

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https://bugs.launchpad.net/bugs/1718761

Title:
  It's not possible to use OverlayFS (mount -t overlay) to stack
  directories on a ZFS volume

Status in linux package in Ubuntu:
  Incomplete

Bug description:
  ---------- Configuration
  # echo -e $(grep VERSION= /etc/os-release)\\nSIGNATURE=\"$(cat 
/proc/version_signature)\"
  VERSION="16.04.3 LTS (Xenial Xerus)"
  SIGNATURE="Ubuntu 4.10.0-35.39~16.04.1-generic 4.10.17"
  # dpkg --list | grep zfs
  ii      libzfs2linux    0.6.5.6-0ubuntu18
  ii      zfs-doc         0.6.5.6-0ubuntu18
  ii      zfs-initramfs   0.6.5.6-0ubuntu18
  ii      zfs-zed         0.6.5.6-0ubuntu18
  ii      zfsutils-linux  0.6.5.6-0ubuntu18

  ---------- Fault: Creating an overlay of multiple directories on a ZFS volume 
does not work
  # df /var/tmp
  Filesystem     Type 1K-blocks  Used Available Use% Mounted on
  tank07/var/tmp zfs  129916288   128 129916160   1% /var/tmp
  # mkdir /var/tmp/{lower,middle,upper,workdir,overlay}
  # mount -t overlay overlay 
-olowerdir=/var/tmp/middle:/var/tmp/lower,upperdir=/var/tmp/upper,workdir=/var/tmp/workdir
 /var/tmp/overlay
  mount: wrong fs type, bad option, bad superblock on overlay,
         missing codepage or helper program, or other error

         In some cases useful info is found in syslog - try
         dmesg | tail or so.
  # dmesg|tail -1
  [276328.438284] overlayfs: filesystem on '/var/tmp/upper' not supported as 
upperdir

  ---------- Control test 1: Creating an overlay of multiple directories on 
another filesystem works
  # df /tmp
  Filesystem     Type  1K-blocks   Used Available Use% Mounted on
  tmpfs          tmpfs   1048576 133492    915084  13% /tmp
  # mkdir /tmp/{lower,middle,upper,workdir,overlay}
  # mount -t overlay overlay 
-olowerdir=/tmp/middle:/tmp/lower,upperdir=/tmp/upper,workdir=/tmp/workdir 
/tmp/overlay
  # mount | grep overlay
  overlay on /tmp/overlay type overlay 
(rw,relatime,lowerdir=/tmp/middle:/tmp/lower,upperdir=/tmp/upper,workdir=/tmp/workdir)

  ---------- Control test 2: Creating an overlay using AuFS works on ZFS volume 
and elsewhere
  # mount -t aufs -obr=/tmp/lower:/tmp/middle:/tmp/upper:/tmp/workdir none 
/tmp/overlay
  # mount -t aufs 
-obr=/var/tmp/lower:/var/tmp/middle:/var/tmp/upper:/var/tmp/workdir none 
/var/tmp/overlay
  # mount | grep aufs
  none on /var/tmp/overlay type aufs (rw,relatime,si=9ead1ecae778b250)
  none on /tmp/overlay type aufs (rw,relatime,si=9ead1ec9257d1250)

  ---------- Remark
  While the use of AuFS can be used as a workaround in the above scenario, AuFS 
in turn will not work with [fuse.]glusterfs mounts (this has been documented 
elsewhere). Given that OverlayFS is part of the (upstream) kernel and Ubuntu 
now officially supports ZFS, the above should be fixed.

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