Bug #5116

Ceph mkimage fails with incompatible rbd features

Added by Gerben Meijer over 3 years ago. Updated about 3 years ago.

Status:PendingStart date:04/19/2017
Priority:NormalDue date:
Assignee:Vlastimil Holer% Done:


Category:Drivers - Storage
Target version:Release 5.6
Resolution: Pull request:
Affected Versions:OpenNebula 5.2, OpenNebula 5.4


mkimage in the Ceph TM driver does an 'rbd map' to create a swap filesystem.

This does not work with all kernels; for example:

[2451939.802702] rbd: image one-10-3-0: image uses unsupported features: 0x38

A possible workaround is to depend on libguestfs and use guestfish to create it. Basic example:

    if [ "$FSTYPE" = "swap" ]; then
        export LIBGUESTFS_BACKEND=direct
        ( echo set-attach-method appliance
          echo add-drive /dev/null
          echo config -set drive.hd0.file=rbd:$RBD_SOURCE
          echo run
          echo mkswap /dev/sda label:swap ) | $SUDO /usr/bin/guestfish

Note that this will also require the addition of /usr/bin/guestfish to sudoers.

I think it's the most elegant solution since it becomes kernel and distro independent.

opennebula-5.2.1-mkswapsparse.diff Magnifier - Patch against OpenNebula 5.2.1 which implements the use of a sparse file, untested (1.11 KB) Roy Keene, 04/19/2017 04:54 PM

mkswap-qemu.sh Magnifier - QEMU-IMG based mkswap (993 Bytes) Roy Keene, 04/19/2017 06:45 PM


#1 Updated by Roy Keene over 3 years ago

A simpler solution is to use "qemu-nbd" to create an NBD that corresponds to the RBD. If QEMU is compiled with RBD support then the QEMU tools have the ability to map RBD devices.

Failing that, it can be done by creating a sparse file and writing the header to it, then reading that header into a new RBD image:

        tmpfile="$(mktemp)" && \
                dd if=/dev/zero of="${tmpfile}" bs=$[1024*1024] seek=$[${SIZE} - 1] count=1 2>/dev/null && \
                mkswap "${tmpfile}" && \
                dd if="${tmpfile}" bs=$(getconf PAGESIZE) count=1 2>/dev/null | rbd import - $RBD && \
                rbd resize --size ${SIZE}M $RBD
        rm -f "${tmpfile}" 

#3 Updated by Roy Keene over 3 years ago

Also attached is a wrapper script called "mkswap-qemu" which uses "qemu-img" to handle both RBD and QCOW2 (and any other format QEMU supports, if properly extended) and run "mkswap"

#4 Updated by Javi Fontan over 3 years ago

  • Target version set to Release 5.6
  • Affected Versions OpenNebula 5.4 added

I'm marking this to be done in the next major release.

#5 Updated by Javi Fontan about 3 years ago

  • Assignee set to Vlastimil Holer

#6 Updated by Tobias Rehn about 3 years ago

We are also experiencing this issue also. I don't think that it is a good idea to create the swap file locally. For virtualization host with small HDDs such a way can fill up the HDD and lead to further issues.

We are using the following workaround:

if [ "$FSTYPE" = "swap" ]; then
    $SUDO $RBD map $RBD_SOURCE --image-feature layering || exit \$?
    $SUDO $MKSWAP -L swap /dev/rbd/$RBD_SOURCE
    $SUDO $RBD unmap /dev/rbd/$RBD_SOURCE

By only using the rbd feature "layering" it works without any issues on older kernels like 3.10 (rhel7 / centos7). Most of the newer features like "deep-flatten", "fast-diff" or "object-map" are only available in newer kernels. Even the latest mainline kernel 4.13 does not support all features. This is because the krbd features are lacking behind the features of rbd.

When using latest ceph luminious you want to use all new features for your images as these have enormous speed enhancements for clones, etc. But you will never ever clone a swap disk - so layering is enough for this type of storage disk.

#7 Updated by Tobias Rehn about 3 years ago

I had a failure in my workaround:

    export PATH=/usr/sbin:/sbin:\$PATH

    if [ "$FSTYPE" = "swap" ]; then
        $RBD create $FORMAT_OPT $RBD_SOURCE --size ${SIZE} --image-feature layering || exit \$?
        $SUDO $RBD map $RBD_SOURCE || exit \$?
        $SUDO $MKSWAP -L swap /dev/rbd/$RBD_SOURCE
        $SUDO $RBD unmap /dev/rbd/$RBD_SOURCE

    $RBD create $FORMAT_OPT $RBD_SOURCE --size ${SIZE} || exit \$?


#8 Updated by Tobias Rehn about 3 years ago

After some further testing I have come the result that I see no advantage from distinguishing between swap or normale volatile disk. I thought the swap disk were automatically mounted but that is not the case and I see no advantage. So we working with the following:

    export PATH=/usr/sbin:/sbin:\$PATH
    $RBD create $FORMAT_OPT $RBD_SOURCE --size ${SIZE} || exit \$?

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