qubes-doc/developer/system/storage-pools.md

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---
lang: en
layout: doc
permalink: /doc/storage-pools/
ref: 57
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title: Storage pools
---
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Qubes OS R3.2 introduced the concept of storage drivers and pools. This feature
was a first step towards a saner storage API, which is heavily rewritten in R4.
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See [here](https://dev.qubes-os.org/projects/core-admin/en/latest/qubes-storage.html)
for documentation on storage pools in R4.
A storage driver provides a way to store VM images in a Qubes OS system.
Currently, the default driver is `xen` which is the default way of storing
volume images as files in a directory tree like `/var/lib/qubes/`.
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A storage pool driver can be identified either by the driver name with the
`driver` key or by the class name like this:
`class=qubes.storage.xen.XenStorage`. Because R3.2 doesn't use Python
`setup_hooks`, to actually use a short driver name for a custom storage driver,
you have to patch `qubes-core-admin`. You can use the `class` config key
instead, when your class is accessible by `import` in Python.
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A pool (in R3.2) is configuration information which can be referenced when
creating a new VM. Each pool is saved in `storage.conf`. It has a name, a
storage driver and some driver specific configuration attached.
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When installed, the system has, as you can see from the contents of
`/etc/qubes/storage.conf`, a pool named `default`. It uses the driver `xen`. The
default pool is special in R3.2. It will add `dir_path=/var/lib/qubes`
configuration value from `defaults[pool_config]`, if not overwritten.
Currently the only supported driver out of the box is `xen`. The benefit of
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pools (besides that you can write your own storage driver e.g. for Btrfs) in R3.2
is that you can store your domains in multiple places.
You can add a pool to `storage.conf` like this:
```
[foo]
driver=xen
dir_path=/opt/qubes-vm
```
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Now, when creating a new VM on the command-line, you may pass the `-Pfoo`
argument to `qvm-create` to have the VM images stored in pool `foo`. See also
`qvm-create --help`.
While the current API is not as clean and beautiful as the R4 API, it allows
you to write your own storage drivers e.g. for Btrfs today.