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 Incus

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

Incus assumes that it has full control over the volume group. Therefore, you should not maintain any file system entities that are not owned by Incus in an LVM volume group, because Incus 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 Incus 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, Incus 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 Incus.

lvmcluster driver in Incus

A second lvmcluster driver is available for use within clusters.

This relies on the lvmlockd and sanlock daemons to provide distributed locking over a shared disk or set of disks.

It allows using a remote shared block device like a FiberChannel LUN, NVMEoF/NVMEoTCP disk or iSCSI drive as the backing for a LVM storage pool.

Note

Thin provisioning is incompatible with clustered LVM, so expect higher disk usage.

To use this with Incus, you must:

• Have a shared block device available on all your cluster members

• Install the relevant packages for lvm, lvmlockd and sanlock

• Enable lvmlockd by setting use_lvmlockd = 1 in your /etc/lvm/lvm.conf

• Set a unique (within your cluster) host_id value in /etc/lvm/lvmlocal.conf

• Ensure that both lvmlockd and sanlock daemons are running

• Create a shared VG and confirm it is accessible on all servers

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

Key	Type	Driver	Default	Description
lvm.thinpool_name	string	lvm	IncusThinPool	Thin pool where volumes are created
lvm.thinpool_metadata_size	string	lvm	0 (auto)	The size of the thin pool metadata volume (the default is to let LVM calculate an appropriate size)
lvm.use_thinpool	bool	lvm	true	Whether the storage pool uses a thin pool for logical volumes
lvm.vg.force_reuse	bool	lvm	false	Force using an existing non-empty volume group
lvm.vg_name	string	all	name of the pool	Name of the volume group to create
rsync.bwlimit	string	all	0 (no limit)	The upper limit to be placed on the socket I/O when rsync must be used to transfer storage entities
rsync.compression	bool	all	true	Whether to use compression while migrating storage pools
size	string	lvm	auto (20% of free disk space, >= 5 GiB and <= 30 GiB)	Size of the storage pool when creating loop-based pools (in bytes, suffixes supported, can be increased to grow storage pool)
source	string	all	-	Path to an existing block device, loop file or LVM volume group
source.wipe	bool	lvm	false	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

Key	Type	Condition	Default	Description
block.filesystem	string	block-based volume with content type filesystem	same as volume.block.filesystem	File system of the storage volume: btrfs, ext4 or xfs (ext4 if not set)
block.mount_options	string	block-based volume with content type filesystem	same as volume.block.mount_options	Mount options for block-backed file system volumes
lvm.stripes	string		same as volume.lvm.stripes	Number of stripes to use for new volumes (or thin pool volume)
lvm.stripes.size	string		same as volume.lvm.stripes.size	Size of stripes to use (at least 4096 bytes and multiple of 512 bytes)
security.shifted	bool	custom volume	same as volume.security.shifted or false	Enable ID shifting overlay (allows attach by multiple isolated instances)
security.unmapped	bool	custom volume	same as volume.security.unmapped or false	Disable ID mapping for the volume
security.shared	bool	custom block volume	same as volume.security.shared or false	Enable sharing the volume across multiple instances
size	string		same as volume.size	Size/quota of the storage volume
snapshots.expiry	string	custom volume	same as volume.snapshots.expiry	Controls when snapshots are to be deleted (expects an expression like 1M 2H 3d 4w 5m 6y)
snapshots.pattern	string	custom volume	same as volume.snapshots.pattern or snap%d	Pongo2 template string that represents the snapshot name (used for scheduled snapshots and unnamed snapshots) [1]
snapshots.schedule	string	custom volume	same as volume.snapshots.schedule	Cron expression (<minute> <hour> <dom> <month> <dow>), a comma-separated list of schedule aliases (@hourly, @daily, @midnight, @weekly, @monthly, @annually, @yearly), or empty to disable automatic snapshots (the default)

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.

Key	Type	Condition	Default	Description
size	string	appropriate driver	same as volume.size	Size/quota of the storage bucket

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[1]

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.