Editing Ploop/Getting started

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

== Requirements == <!--T:2-->

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The following is required for ploop to work:

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# [[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 NFSv3. No other filesystem is supported.
# ploop library and tools installed (run <code>yum install ploop</code>).

== Making a CT on ploop == <!--T:5-->

=== Global configuration === <!--T:6-->

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

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VE_LAYOUT=ploop 

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

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

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

=== Creating a new CT === <!--T:12-->

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To create a new container on ploop, use:

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

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# 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 === <!--T:16-->

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

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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

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3. Convert:
 vzctl convert ''CTID''

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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 == <!--T:21-->

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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.

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To resize a ploop CT image, use

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

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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 '''--diskinodes''' is ignored). See [[../diskinodes/]] for more details

== Showing disk space usage / limits == <!--T:26-->

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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).

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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).

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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).

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Examples:

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

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

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

== Using disk quotas inside container == <!--T:34-->

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

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

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Note that:
* unlike with simfs, ''--quotaugidlimit'' argument can be any non-zero value;
* enabling or disabling in-container disk quotas requires a container restart, so you can use vzctl's '''--setmode''' option.

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

== See also == <!--T:39-->

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