Storage Plugin Development
Proxmox VE has a generic storage plugin system; in addition to the natively included plugins, there's also a mechanism for loading external third-party plugins.
This wiki provides some basic documentation on how to develop plugins and important rules to follow when doing so.
Licensing
Your storage plugin code will be loaded by the AGPLv3+ licensed Proxmox VE system and therefore needs to be licensed to allow this.
Note that this only affects the plugin code itself, not the source code of your actual storage system. To interface with proprietary code, you can, for example, run external binaries, use a (public) network API (such as over HTTP), or use a separate client library released under an AGPLv3+-compatible license.
It's strongly recommended that you use one of the following three licenses for the plugin code, in order of preference:
Proxmox Server Solutions GmbH reserves the right to take legal action and/or actively break any external plugin if it is licensed under a proprietary license or one that does not comply with being combined into an AGPLv3+ project.
Plugin Architecture
Language Support
Plugins are Perl modules. Note that you can also create Perl bindings for other language, like through Perl XS for C FFI/libraries or the Proxmox perlmod crate for rust based projects.
Loading Path
External Plugins are loaded from /usr/share/perl5/PVE/Storage/Custom/YourCustomPlugin.pm, and thus they must have a Perl package declaration like package PVE::Storage::Custom::YourCustomPlugin;
We recommend that you release your storage plugin for Proxmox VE as Debian package. Doing so nicely integrates with how Proxmox VE is updated including declaring version dependencies or constraints with other packages.
API Versioning
The storage plugin API versioning contains an APIVER and an APIAGE.
The APIAGE is the number of versions we're backward compatible with. (in other words, things got added without breaking anything unaware of it.)
The API version changelog is tracked in the pve-storage git repository: https://git.proxmox.com/?p=pve-storage.git;a=blob;f=ApiChangeLog;h=98b58938ab41cd15aacbd307db51450bfa4b631f;hb=98a5bc5c9b5a030cef88629900cc1214120feb61
API
In general, it's highly recommended to base your plugin of an included plugin, if unsure use the base plugin or the one your storage has the most similarities with.
For example through:
use base qw(PVE::Storage::Plugin);
All (included) plugins are basing of the Proxmox SectionConfig module. If you decide to roll your own base for your plugin you need to ensure manually that you're compatible with the SectionConfig API.
You must at least implement the following sub-methods:
api- return theAPIVERversion your plugin supports.type- returns the storage section config string type that identifies your storage type.plugindata- returns an object with metadata about what content types, formats and defaults your storage plugin supports.properties- returns a schema of (additional) properties that your plugin needs or wants to support as configuration.option- returns a schema of the options that your plugin understands, with specifying if they are optional or not. Note that the properties of all other plugins are available for use too.
Then implement any sub-method with a $class as first argument from the base-plugin for which you need a storage-specific behavior.
Note: This section should be expanded, for now see the examples below and checkout the existing included plugins and the section config source.
Examples
For some examples of real-world third party storage plugins see the following links:
https://github.com/LINBIT/linstor-proxmox/blob/master/LINSTORPlugin.pm
https://github.com/storpool/pve-storpool/blob/main/lib/PVE/Storage/Custom/StorPoolPlugin.pm
Support and Help
While Proxmox does not offer paid support or even development work for creating external storage plugins, you can ask any development related question on our mailing list.
Please ask specific questions and provide your (work in progress) code, ideally as git repository.