fix #3884: Add section for kernel samepage merging

[pve-docs.git] / pve-storage-dir.adoc

[[storage_directory]]
Directory Backend
-----------------
ifdef::wiki[]
:pve-toplevel:
:title: Storage: Directory
endif::wiki[]

Storage pool type: `dir`

{pve} can use local directories or locally mounted shares for
storage. A directory is a file level storage, so you can store any
content type like virtual disk images, containers, templates, ISO images
or backup files.

NOTE: You can mount additional storages via standard linux `/etc/fstab`,
and then define a directory storage for that mount point. This way you
can use any file system supported by Linux.

This backend assumes that the underlying directory is POSIX
compatible, but nothing else. This implies that you cannot create
snapshots at the storage level. But there exists a workaround for VM
images using the `qcow2` file format, because that format supports
snapshots internally.

TIP: Some storage types do not support `O_DIRECT`, so you can't use
cache mode `none` with such storages. Simply use cache mode
`writeback` instead.

We use a predefined directory layout to store different content types
into different sub-directories. This layout is used by all file level
storage backends.

.Directory layout
[width="100%",cols="d,m",options="header"]
|===========================================================
|Content type        |Subdir
|VM images           |`images/<VMID>/`
|ISO images          |`template/iso/`
|Container templates |`template/cache/`
|Backup files        |`dump/`
|Snippets            |`snippets/`
|===========================================================


Configuration
~~~~~~~~~~~~~

This backend supports all common storage properties, and adds an
additional property called `path` to specify the directory. This
needs to be an absolute file system path.

.Configuration Example (`/etc/pve/storage.cfg`)
----
dir: backup
        path /mnt/backup
        content backup
        prune-backups keep-last=7
        max-protected-backups 3
----

The above configuration defines a storage pool called `backup`. That pool can be
used to store up to 7 regular backups (`keep-last=7`) and 3 protected backups
per VM. The real path for the backup files is `/mnt/backup/dump/...`.


File naming conventions
~~~~~~~~~~~~~~~~~~~~~~~

This backend uses a well defined naming scheme for VM images:

 vm-<VMID>-<NAME>.<FORMAT>
 
`<VMID>`::

This specifies the owner VM.

`<NAME>`::

This can be an arbitrary name (`ascii`) without white space. The
backend uses `disk-[N]` as default, where `[N]` is replaced by an
integer to make the name unique.

`<FORMAT>`::

Specifies the image format (`raw|qcow2|vmdk`).

When you create a VM template, all VM images are renamed to indicate
that they are now read-only, and can be used as a base image for clones:

 base-<VMID>-<NAME>.<FORMAT>

NOTE: Such base images are used to generate cloned images. So it is
important that those files are read-only, and never get modified. The
backend changes the access mode to `0444`, and sets the immutable flag
(`chattr +i`) if the storage supports that.


Storage Features
~~~~~~~~~~~~~~~~

As mentioned above, most file systems do not support snapshots out
of the box. To workaround that problem, this backend is able to use
`qcow2` internal snapshot capabilities.

Same applies to clones. The backend uses the `qcow2` base image
feature to create clones.

.Storage features for backend `dir`
[width="100%",cols="m,m,3*d",options="header"]
|==============================================================================
|Content types                              |Image formats         |Shared |Snapshots |Clones
|images rootdir vztmpl iso backup snippets  |raw qcow2 vmdk subvol |no     |qcow2     |qcow2
|==============================================================================


Examples
~~~~~~~~

Please use the following command to allocate a 4GB image on storage `local`:

 # pvesm alloc local 100 vm-100-disk10.raw 4G
 Formatting '/var/lib/vz/images/100/vm-100-disk10.raw', fmt=raw size=4294967296
 successfully created 'local:100/vm-100-disk10.raw'

NOTE: The image name must conform to above naming conventions.

The real file system path is shown with:

 # pvesm path local:100/vm-100-disk10.raw
 /var/lib/vz/images/100/vm-100-disk10.raw

And you can remove the image with:

 # pvesm free local:100/vm-100-disk10.raw


ifdef::wiki[]

See Also
~~~~~~~~

* link:/wiki/Storage[Storage]

endif::wiki[]