LVM - lvm

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.shared

Enable volume sharing

Key: security.shared
Type:

bool

Default:

same as volume.security.shared or false

Condition:

custom block volume

Enabling this option allows sharing the volume across multiple instances despite the possibility of data loss.

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