Synnefo » snf-ganeti » ganeti-local

ganeti-extstorage-interface(7) Ganeti | Version @GANETI_VERSION@

================================================================

Name

----

ganeti-extstorage-interface - Specifications for ExtStorage providers

DESCRIPTION

-----------

The method for supporting external shared storage in Ganeti is to have

an ExtStorage provider for each external shared storage hardware type.

The ExtStorage provider is a set of files (executable scripts and text

files), contained inside a directory which is named after the provider.

This directory must be present across all nodes of a nodegroup (Ganeti

doesn't replicate it), in order for the provider to be usable by Ganeti

for this nodegroup (valid). The external shared storage hardware should

also be accessible by all nodes of this nodegroup too.

REFERENCE

---------

There are eight required files: *create*, *attach*, *detach*, *remove*,

*grow*, *setinfo*, *verify* (executables) and *parameters.list*

(text file).

Common environment

~~~~~~~~~~~~~~~~~~

All commands will get their input via environment variables. A common

set of variables will be exported for all commands, and some of them

might have extra ones. Note that all counts are zero-based.

Since Ganeti version 2.5, the environment will be cleaned up before

being passed to scripts, therefore they will not inherit the environment

in with which the ganeti node daemon was started. If you depend on any

environment variables (non-Ganeti), then you will need to define or

source them appropriately.

VOL_NAME

    The name of the volume. This is unique for Ganeti and it uses it

    to refer to a specific volume inside the external storage. Its

    format is ``UUID.ext.diskX`` where ``UUID`` is produced by Ganeti

    and is unique inside the Ganeti context. ``X`` is the number of the

    disk count.

VOL_SIZE

    The volume's size in mebibytes.

VOL_NEW_SIZE

    Available only to the **grow** script. It declares the new size of

    the volume after grow (in mebibytes). To find the amount of grow,

    the scipt should calculate the number VOL_NEW_SIZE - VOL_SIZE.

EXTP_*name*

    Each ExtStorage parameter (see below) will be exported in its own

    variable, prefixed with ``EXTP_``, and upper-cased. For example, a

    ``fromsnap`` parameter will be exported as ``EXTP_FROMSNAP``.

VOL_METADATA

    Available only to the **setinfo** script. A string containing

    metadata to be associated with the volume. Currently, Ganeti sets

    this value to ``originstname+X`` where ``X`` is the instance's name.

EXECUTABLE SCRIPTS

------------------

create

~~~~~~

The **create** command is used for creating a new volume inside the

external storage. The ``VOL_NAME`` denotes the volume's name, which

should be unique. After creation, Ganeti will refer to this volume by

this name for all other actions.

Ganeti produces this name dynamically and ensures its uniqueness inside

the Ganeti context. Therefore, you should make sure not to provision

manually additional volumes inside the external storage with this type

of name, because this will lead to conflicts and possible loss of data.

The ``VOL_SIZE`` variable denotes the size of the new volume to be

created in mebibytes.

If the script ends successfully, a new volume of size ``VOL_SIZE``

should exist inside the external storage. e.g:: a lun inside a NAS

appliance.

The script returns ``0`` on success.

attach

~~~~~~

This command is used in order to make an already created volume visible

to the physical node which will host the instance. This is done by

mapping the already provisioned volume to a block device inside the host

node.

The ``VOL_NAME`` variable denotes the volume to be mapped.

After successful attachment the script returns to its stdout a string,

which is the full path of the block device to which the volume is

mapped.  e.g:: /dev/dummy1

When attach returns, this path should be a valid block device on the

host node.

The attach script should be idempotent if the volume is already mapped.

If the requested volume is already mapped, then the script should just

return to its stdout the path which is already mapped to.

detach

~~~~~~

This command is used in order to unmap an already mapped volume from the

host node. Detach undoes everything attach did. This is done by

unmapping the requested volume from the block device it is mapped to.

The ``VOL_NAME`` variable denotes the volume to be unmapped.

``detach`` doesn't affect the volume itself. It just unmaps it from the

host node. The volume continues to exist inside the external storage.

It's just not accessible by the node anymore. This script doesn't return

anything to its stdout.

The detach script should be idempotent if the volume is already

unmapped. If the volume is not mapped, the script doesn't perform any

action at all.

The script returns ``0`` on success.

remove

~~~~~~

This command is used to remove an existing volume from the external

storage. The volume is permanently removed from inside the external

storage along with all its data.

The ``VOL_NAME`` variable denotes the volume to be removed.

The script returns ``0`` on success.

grow

~~~~

This command is used to grow an existing volume of the external storage.

The ``VOL_NAME`` variable denotes the volume to grow.

The ``VOL_SIZE`` variable denotes the current volume's size (in

mebibytes). The ``VOL_NEW_SIZE`` variable denotes the final size after

the volume has been grown (in mebibytes).

The amount of grow can be easily calculated by the scipt and is:

grow_amount = VOL_NEW_SIZE - VOL_SIZE (in mebibytes)

Ganeti ensures that: ``VOL_NEW_SIZE`` > ``VOL_SIZE``

If the script returns successfully, then the volume inside the external

storage will have a new size of ``VOL_NEW_SIZE``. This isn't immediately

reflected to the instance's disk. See ``gnt-instance grow`` for more

details on when the running instance becomes aware of its grown disk.

The script returns ``0`` on success.

setinfo

~~~~~~~

This script is used to add metadata to an existing volume. It is helpful

when we need to keep an external, Ganeti-independent mapping between

instances and volumes; primarily for recovery reasons. This is provider

specific and the author of the provider chooses whether/how to implement

this. You can just exit with ``0``, if you do not want to implement this

feature, without harming the overall functionality of the provider.

The ``VOL_METADATA`` variable contains the metadata of the volume.

Currently, Ganeti sets this value to ``originstname+X`` where ``X`` is

the instance's name.

The script returns ``0`` on success.

verify

~~~~~~

The *verify* script is used to verify consistency of the external

parameters (ext-params) (see below). The command should take one or more

arguments denoting what checks should be performed, and return a proper

exit code depending on whether the validation failed or succeeded.

Currently, the script is not invoked by Ganeti, but should be present

for future use and consistency with gnt-os-interface's verify script.

The script should return ``0`` on success.

TEXT FILES

----------

parameters.list

~~~~~~~~~~~~~~~

This file declares the parameters supported by the ExtStorage provider,

one parameter per line, with name and description (space and/or tab

separated). For example::

    fromsnap Snapshot name to create the volume from

    nas_ip The IP of the NAS appliance

The parameters can then be used during instance add as follows::

    # gnt-instance add --disk=0:fromsnap="file_name",nas_ip="1.2.3.4" ...

NOTES

-----

Backwards compatibility

~~~~~~~~~~~~~~~~~~~~~~~

The ExtStorage Interface was introduced in Ganeti 2.7.

Ganeti 2.7 and up is compatible with the ExtStorage Interface.

Common behaviour

~~~~~~~~~~~~~~~~

All the scripts should display an usage message when called with a wrong

number of arguments or when the first argument is ``-h`` or ``--help``.

.. vim: set textwidth=72 :

.. Local Variables:

.. mode: rst

.. fill-column: 72

.. End: