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 (quota) 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 (quota) 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¶
| Key: | lvm.thinpool_metadata_size |
| Type: | string |
| Default: |
|
| Scope: | global |
By default, LVM calculates an appropriate size.
| Key: | lvm.thinpool_name |
| Type: | string |
| Default: |
|
| Scope: | local |
| Key: | lvm.use_thinpool |
| Type: | bool |
| Default: |
|
| Scope: | global |
| Key: | lvm.vg.force_reuse |
| Type: | bool |
| Default: |
|
| Scope: | global |
| Key: | lvm.vg_name |
| Type: | string |
| Default: | name of the pool |
| Scope: | local |
| Key: | rsync.bwlimit |
| Type: | string |
| Default: |
|
| Scope: | global |
When rsync must be used to transfer storage entities, this option specifies the upper limit
to be placed on the socket I/O.
| Key: | rsync.compression |
| Type: | bool |
| Default: |
|
| Scope: | global |
| Key: | size |
| Type: | string |
| Default: | auto (20% of free disk space, >= 5 GiB and <= 30 GiB) |
| Scope: | local |
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.
| Key: | source |
| Type: | string |
| Scope: | local |
| Key: | source.wipe |
| Type: | bool |
| Default: |
|
| Scope: | local |
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¶
| Key: | block.filesystem |
| Type: | string |
| Default: | same as |
| Condition: | block-based volume with content type |
| Scope: | global |
Valid options are: btrfs, ext4, xfs
If not set, ext4 is assumed.
| Key: | block.mount_options |
| Type: | string |
| Default: | same as |
| Condition: | block-based volume with content type |
| Scope: | global |
| Key: | lvm.stripes |
| Type: | string |
| Default: | same as |
| Scope: | global |
| Key: | lvm.stripes.size |
| Type: | string |
| Default: | same as |
| Scope: | global |
The size must be at least 4096 bytes, and a multiple of 512 bytes.
| Key: | security.shifted |
| Type: | bool |
| Default: | same as |
| Condition: | custom volume |
| Scope: | global |
Enabling this option allows attaching the volume to multiple isolated instances.
| Key: | security.unmapped |
| Type: | bool |
| Default: | same as |
| Condition: | custom volume |
| Scope: | global |
| Key: | size |
| Type: | string |
| Default: | same as |
| Condition: | appropriate driver |
| Scope: | global |
| Key: | snapshots.expiry |
| Type: | string |
| Default: | same as |
| Condition: | custom volume |
| Scope: | global |
Specify an expression like 1M 2H 3d 4w 5m 6y.
| Key: | snapshots.pattern |
| Type: | string |
| Default: | same as |
| Condition: | custom volume |
| Scope: | global |
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.
| Key: | snapshots.schedule |
| Type: | string |
| Default: | same as |
| Condition: | custom volume |
| Scope: | global |
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).
| Key: | volatile.idmap.last |
| Type: | string |
| Condition: | filesystem |
| Key: | volatile.idmap.next |
| Type: | string |
| Condition: | filesystem |
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.