LVM - lvm
Description: LVM is a storage management framework rather than a file system. It is used to manage physical storage devices, allowing you to create a number of logical storage volumes that use and virtualize th...

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# LVM - `lvm`

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LVM is a storage management framework rather than a file system. It is used to manage physical storage devices, allowing you to create a number of logical storage volumes that use and virtualize the underlying physical storage devices.

Note that it is possible to over-commit the physical storage in the process, to allow flexibility for scenarios where not all available storage is in use at the same time.

To use LVM, make sure you have `lvm2` installed on your machine.

## Terminology

LVM can combine several physical storage devices into a volume group. You can then allocate logical volumes of different types from this volume group.

One supported volume type is a thin pool, which allows over-committing the resources by creating thinly provisioned volumes whose total allowed maximum size is larger than the available physical storage. Another type is a volume snapshot, which captures a specific state of a logical volume.

## `lvm` driver in LXD

The `lvm` driver in LXD uses logical volumes for images, and volume snapshots for instances and snapshots.

LXD assumes that it has full control over the volume group. Therefore, you should not maintain any file system entities that are not owned by LXD in an LVM volume group, because LXD might delete them. However, if you need to reuse an existing volume group (for example, because your setup has only one volume group), you can do so by setting the `lvm.vg.force_reuse` configuration.

By default, LVM storage pools use an LVM thin pool and create logical volumes for all LXD storage entities (images, instances and custom volumes) in there. This behavior can be changed by setting `lvm.use_thinpool` to `false` when you create the pool. In this case, LXD uses “normal” logical volumes for all storage entities that are not snapshots. Note that this entails serious performance and space reductions for the `lvm` driver (close to the `dir` driver both in speed and storage usage). The reason for this is that most storage operations must fall back to using `rsync`, because logical volumes that are not thin pools do not support snapshots of snapshots. In addition, non-thin snapshots take up much more storage space than thin snapshots, because they must reserve space for their maximum size at creation time. Therefore, this option should only be chosen if the use case requires it.

For environments with a high instance turnover (for example, continuous integration) you should tweak the backup `retain_min` and `retain_days` settings in `/etc/lvm/lvm.conf` to avoid slowdowns when interacting with LXD.

## Configuration options

The following configuration options are available for storage pools that use the `lvm` driver and for storage volumes in these pools.

### Storage pool configuration

`lvm.thinpool_metadata_size`

The size of the thin pool metadata volume

Key: | `lvm.thinpool_metadata_size`
Type: | string
Default: | `0` (auto)

By default, LVM calculates an appropriate size.

`lvm.thinpool_name`

Thin pool where volumes are created

Key: | `lvm.thinpool_name`
Type: | string
Default: | `LXDThinPool`

`lvm.use_thinpool`

Whether the storage pool uses a thin pool for logical volumes

Key: | `lvm.use_thinpool`
Type: | bool
Default: | `true`

`lvm.vg.force_reuse`

Force using an existing non-empty volume group

Key: | `lvm.vg.force_reuse`
Type: | bool
Default: | `false`

`lvm.vg_name`

Name of the volume group to create

Key: | `lvm.vg_name`
Type: | string
Default: | name of the pool

`rsync.bwlimit`

Upper limit on the socket I/O for `rsync`

Key: | `rsync.bwlimit`
Type: | string
Default: | `0` (no limit)

When `rsync` must be used to transfer storage entities, this option specifies the upper limit to be placed on the socket I/O.

`rsync.compression`

Whether to use compression while migrating storage pools

Key: | `rsync.compression`
Type: | bool
Default: | `true`

`size`

Size of the storage pool (for loop-based pools)

Key: | `size`
Type: | string
Default: | auto (20% of free disk space, >= 5 GiB and <= 30 GiB)

When creating loop-based pools, specify the size in bytes (suffixes are supported). You can increase the size to grow the storage pool.

The default (`auto`) creates a storage pool that uses 20% of the free disk space, with a minimum of 5 GiB and a maximum of 30 GiB.

`source`

Path to an existing block device, loop file, or LVM volume group

Key: | `source`
Type: | string

`source.wipe`

Whether to wipe the block device before creating the pool

Key: | `source.wipe`
Type: | bool
Default: | `false`

Set this option to `true` to wipe the block device specified in `source` prior to creating the storage pool.

Tip

In addition to these configurations, you can also set default values for the storage volume configurations. See Configure default values for storage volumes.

### Storage volume configuration

`block.filesystem`

File system of the storage volume

Key: | `block.filesystem`
Type: | string
Default: | same as `volume.block.filesystem`
Condition: | block-based volume with content type `filesystem`

Valid options are: `btrfs`, `ext4`, `xfs` If not set, `ext4` is assumed.

`block.mount_options`

Mount options for block-backed file system volumes

Key: | `block.mount_options`
Type: | string
Default: | same as `volume.block.mount_options`
Condition: | block-based volume with content type `filesystem`

`lvm.stripes`

Number of stripes to use for new volumes (or thin pool volume)

Key: | `lvm.stripes`
Type: | string
Default: | same as `volume.lvm.stripes`

`lvm.stripes.size`

Size of stripes to use

Key: | `lvm.stripes.size`
Type: | string
Default: | same as `volume.lvm.stripes.size`

The size must be at least 4096 bytes, and a multiple of 512 bytes.

`security.shifted`

Enable ID shifting overlay

Key: | `security.shifted`
Type: | bool
Default: | same as `volume.security.shifted` or `false`
Condition: | custom volume

Enabling this option allows attaching the volume to multiple isolated instances.

`security.unmapped`

Disable ID mapping for the volume

Key: | `security.unmapped`
Type: | bool
Default: | same as `volume.security.unmappped` or `false`
Condition: | custom volume

`size`

Size/quota of the storage volume

Key: | `size`
Type: | string
Default: | same as `volume.size`
Condition: | appropriate driver

`snapshots.expiry`

When snapshots are to be deleted

Key: | `snapshots.expiry`
Type: | string
Default: | same as `volume.snapshots.expiry`
Condition: | custom volume

Specify an expression like `1M 2H 3d 4w 5m 6y`.

`snapshots.pattern`

Template for the snapshot name

Key: | `snapshots.pattern`
Type: | string
Default: | same as `volume.snapshots.pattern` or `snap%d`
Condition: | custom volume

You can specify a naming template that is used for scheduled snapshots and unnamed snapshots.

The `snapshots.pattern` option takes a Pongo2 template string to format the snapshot name.

To add a time stamp to the snapshot name, use the Pongo2 context variable `creation_date`. Make sure to format the date in your template string to avoid forbidden characters in the snapshot name. For example, set `snapshots.pattern` to `{{ creation_date|date:'2006-01-02_15-04-05' }}` to name the snapshots after their time of creation, down to the precision of a second.

Another way to avoid name collisions is to use the placeholder `%d` in the pattern. For the first snapshot, the placeholder is replaced with `0`. For subsequent snapshots, the existing snapshot names are taken into account to find the highest number at the placeholder’s position. This number is then incremented by one for the new name.

`snapshots.schedule`

Schedule for automatic volume snapshots

Key: | `snapshots.schedule`
Type: | string
Default: | same as `snapshots.schedule`
Condition: | custom volume

Specify either a cron expression (`<minute> <hour> <dom> <month> <dow>`), a comma-separated list of schedule aliases (`@hourly`, `@daily`, `@midnight`, `@weekly`, `@monthly`, `@annually`, `@yearly`), or leave empty to disable automatic snapshots (the default).

`volatile.uuid`

The volume’s UUID

Key: | `volatile.uuid`
Type: | string
Default: | random UUID

### Storage bucket configuration

To enable storage buckets for local storage pool drivers and allow applications to access the buckets via the S3 protocol, you must configure the `core.storage_buckets_address` server setting.

`size`

Size/quota of the storage bucket

Key: | `size`
Type: | string
Default: | same as `volume.size`
Condition: | appropriate driver