Editing Ploop/Getting started

This article describes how to use container-in-a-file technology aka [[ploop]]

== Requirements ==

The following is required for ploop to work:

# [[Download/kernel/rhel6|RHEL6-based OpenVZ kernel]], i.e. 042stabXXX.
# <code>/vz</code> partition formatted as <code>ext4</code> and mounted in ordered mode, or residing on NFS. No other filesystem is supported.
# ploop library and tools installed (run <code>yum install ploop</code>).

== Making a CT on ploop ==

=== Global configuration ===

In global VZ configuration file [[Man/vz.conf.5|/etc/vz/vz.conf]], set

 VE_LAYOUT=ploop 

This means that all new containers you will create will have ploop layout by default.

You don't have to set this option if you don't want ploop to be default. Alternatively, you can:

* use <code>--layout</code> option of <code>vzctl create</code> command;
* convert existing container to ploop.

=== Creating a new CT ===

To create a new container on ploop, use:

 vzctl create ''CTID'' [--layout ploop] [--diskspace ''nnn''G] [--diskinodes ''mmm'']

# You can omit <code>--layout</code> option if you have set <code>VE_LAYOUT=ploop</code> in {{Man|vz.conf|5}}
# You can specify initial file system size using <code>--diskspace</code> option (example: 10G for 10 gigabytes)
# If <code>--diskspace</code> is not specified, the size defaults to DISKSPACE limit value in sample CT config used
# If <code>--diskinodes</code> is not specified, 1 inode per 16K of disk space will be created (see [[../diskinodes/]] for more info)

=== Converting an existing CT ===

1. Stop the container:
 vzctl stop ''CTID''

2. Set some sane diskspace value, and reset the [[../diskinodes/]] value. New value for diskspace will be used as a size of newly created ploop image. Here is the example to set diskspace to 10 gigabytes:
 vzctl set ''CTID'' --diskspace 10G --diskinodes 0 --save

3. Convert:
 vzctl convert ''CTID''

4. Once your CT is well tested, you can free disk space by removing files that may have remained from the old container file system in /vz/root/''CTID''. VERY CAREFULLY (and after testing your converted container) you can stop, remove old files and start container again, e.g.:
 vzctl stop ''CTID''
 rm -rf /vz/root/''CTID'';mkdir /vz/root/''CTID''
 vzctl start ''CTID''

== Resizing a ploop image ==

Ploop image can be resized in both directions (i.e. either shrank or grown). Ploop also supports online/live resize so you don't have to stop a CT to do resize.

To resize a ploop CT image, use

 vzctl set ''CTID'' --diskspace ''nnn''G --save

Note that
* resize can safely be performed online (i.e. when container is running)
* there is no need to specify two values for diskspace (unlike simfs, there is no soft and hard quota).
* there is no way to limit or change the number of inodes available for an existing container (i.e. option <code>--diskinodes</code> is ignored); see [[../diskinodes/]] for more details

== Showing disk space usage / limits ==

You can use {{Man|vzlist|8}} to see CT disk space usage and limits in a uniform way for any containers (simfs or ploop, started or stopped).

The field '''diskspace''' is showing the current disk space usage, and the fields '''diskspace.s''' and '''diskspace.h''' are showing the filesystem size (or disk space quotas, for simfs case).

The field '''diskinodes''' is showing the current inodes usage, and the fields '''diskinodes.s''' and '''diskinodes.h''' are showing the filesystem size (or disk inodes quotas, for simfs case).

Examples:

 vzlist -o smart_name,diskspace.h,diskspace
 vzlist -o smart_name,diskinodes.h,diskinodes

On a lower level, same info can be obtained via '''ploop info''' command:

 ploop info /vz/private/501/root.hdd/DiskDescriptor.xml

== Using disk quotas inside container ==

If you want to use standard Linux per-user and per-group disk quota inside a container, you have to enable it using

 vzctl set ''CTID'' --quotaugidlimit 1000 --save

Note that:
* unlike with simfs, <code>--quotaugidlimit</code> argument can be any non-zero value;
* enabling or disabling in-container disk quotas requires a container restart, so you might find <code>--setmode</code> option helpful.

See {{Man|vzctl|8}} for more details.

== See also ==

* [[Ploop]]
* [[Ploop/backup]]
* {{Man|ploop|8}}
* {{Man|vz.conf|5}}
* {{Man|vzctl|8}}

[[Category: Storage]]
[[Category: HOWTO]]