Article ID: 115201, created on Nov 26, 2012, last review on Jun 22, 2016

  • Applies to:
  • Virtuozzo 6.0


After upgrading to Parallels Cloud Server 6.0, it is impossible to create a ploop-based container.

The creation process fails with the following error:
[root@pcs ~]# prlctl create 101 --ostemplate centos-6-x86_64 --vmtype ct
Creating the Virtuozzo Container...
Failed to register the CT: Operation failed. The ploop image can not be used on ext3 or ext4 file system without extents.
Failed to resize image: The ploop image can not be used on ext3 or ext4 file system without extents. [21]


ploop is a new container layout/technology represented in Parallels Cloud Server 6.0. It is mandatory to have the /vz/ partition file system formatted as ext4.

The upgrade process doesn't convert partitions, which means that if /vz/ was formatted as ext3 before the upgrade, it will be the same after the upgrade.

The file system must be formatted manually (can be done before the upgrade).

IMPORTANT NOTE: It is not enough to remount ext3 as ext4; the complete conversion is necessary.


To be able to create a ploop container, you need to convert your /vz/ partition file system type to ext4.

The file system can be converted by following the official steps from the wiki Ext 4 Howto: Converting an ext3 filesystem to ext4:
  1. Stop virtualization services:
    [root@pcs ~]# service vz stop
    [root@pcs ~]# service parallels-server stop
  2. Remove /vz/pfcache.hdd partition:
    [root@pcs ~]# rm -rf /vz/pfcache.hdd
  3. Unmount /vz/ partition:
    [root@pcs ~]# umount /vz
  4. Convert the file system:
    [root@pcs ~]# tune2fs -O extents,uninit_bg,dir_index /dev/DEVICE_NAME
    [root@pcs ~]# e2fsck -fDC0 /dev/DEVICE_NAME
    (This command will ask if you would like to fix errors; press Y to continue.)
  5. Change mounting options in /etc/fstab:
    [root@pcs ~]# mount /dev/DEVICE_NAME /vz
    [root@pcs ~]# grep "/vz" /etc/fstab
    /dev/DEVICE_NAME /vz                     ext3    defaults,noatime 1 2
    [root@pcs ~]# vi /etc/fstab
    [root@pcs ~]# grep "/vz" /etc/fstab
    /dev/DEVICE_NAME /vz                     ext4    defaults,noatime 1 2
  6. Start virtualization services:
    [root@pcs ~]# service parallels-server start
    [root@pcs ~]# service vz start
NOTE: Replace DEVICE_NAME with the actual partition name.

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