How to manage storage volumes

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See the following sections for instructions on how to create, configure, view and resize Storage volumes.

Create a custom storage volume

When you create an instance, LXD automatically creates a storage volume that is used as the root disk for the instance.

You can add custom storage volumes to your instances. Such custom storage volumes are independent of the instance, which means that they can be backed up separately and are retained until you delete them. Custom storage volumes with content type filesystem can also be shared between different instances.

See Storage volumes for detailed information.

Create the volume

Use the following command to create a custom storage volume of type block or filesystem in a storage pool:

lxc storage volume create <pool_name> <volume_name> [configuration_options...]

See the Storage drivers documentation for a list of available storage volume configuration options for each driver.

By default, custom storage volumes use the filesystem content type. To create a custom storage volume with the content type block, add the --type flag:

lxc storage volume create <pool_name> <volume_name> --type=block [configuration_options...]

To add a custom storage volume on a cluster member, add the --target flag:

lxc storage volume create <pool_name> <volume_name> --target=<cluster_member> [configuration_options...]

Note

For most storage drivers, custom storage volumes are not replicated across the cluster and exist only on the member for which they were created. This behavior is different for Ceph-based storage pools (ceph and cephfs), where volumes are available from any cluster member.

To create a custom storage volume of type iso, use the import command instead of the create command:

lxc storage volume import <pool_name> <iso_path> <volume_name> --type=iso

Attach the volume to an instance

After creating a custom storage volume, you can add it to one or more instances as a disk device.

The following restrictions apply:

  • Custom storage volumes of content type block or iso cannot be attached to containers, but only to virtual machines.

  • To avoid data corruption, storage volumes of content type block should never be attached to more than one virtual machine at a time.

  • Storage volumes of content type iso are always read-only, and can therefore be attached to more than one virtual machine at a time without corrupting data.

  • File system storage volumes can’t be attached to virtual machines while they’re running.

  • Custom block storage volumes that don’t have security.shared enabled cannot be attached to more than one instance at the same time and neither can be attached to profiles.

For custom storage volumes with the content type filesystem, use the following command, where <location> is the path for accessing the storage volume inside the instance (for example, /data):

lxc storage volume attach <pool_name> <filesystem_volume_name> <instance_name> <location>

Custom storage volumes with the content type block do not take a location:

lxc storage volume attach <pool_name> <block_volume_name> <instance_name>

By default, the custom storage volume is added to the instance with the volume name as the device name. If you want to use a different device name, you can add it to the command:

lxc storage volume attach <pool_name> <filesystem_volume_name> <instance_name> <device_name> <location>
lxc storage volume attach <pool_name> <block_volume_name> <instance_name> <device_name>

Attach the volume as a device

The lxc storage volume attach command is a shortcut for adding a disk device to an instance. Alternatively, you can add a disk device for the storage volume in the usual way:

lxc config device add <instance_name> <device_name> disk pool=<pool_name> source=<volume_name> [path=<location>]

When using this way, you can add further configuration to the command if needed. See disk device for all available device options.

Configure I/O limits

When you attach a storage volume to an instance as a disk device, you can configure I/O limits for it. To do so, set the limits.read, limits.write or limits.max properties to the corresponding limits. See the Type: disk reference for more information.

The limits are applied through the Linux blkio cgroup controller, which makes it possible to restrict I/O at the disk level (but nothing finer grained than that).

Note

Because the limits apply to a whole physical disk rather than a partition or path, the following restrictions apply:

  • Limits will not apply to file systems that are backed by virtual devices (for example, device mapper).

  • If a file system is backed by multiple block devices, each device will get the same limit.

  • If two disk devices that are backed by the same disk are attached to the same instance, the limits of the two devices will be averaged.

All I/O limits only apply to actual block device access. Therefore, consider the file system’s own overhead when setting limits. Access to cached data is not affected by the limit.

Use the volume for backups or images

Instead of attaching a custom volume to an instance as a disk device, you can also use it as a special kind of volume to store backups or images.

To do so, you must set the corresponding server configuration:

  • To use a custom volume to store the backup tarballs:

    lxc config set storage.backups_volume <pool_name>/<volume_name>

  • To use a custom volume to store the image tarballs:

    lxc config set storage.images_volume <pool_name>/<volume_name>

Configure storage volume settings

See the Storage drivers documentation for the available configuration options for each storage driver.

Use the following command to set configuration options for a storage volume:

lxc storage volume set <pool_name> [<volume_type>/]<volume_name> <key> <value>

The default storage volume type is custom, so you can leave out the <volume_type>/ when configuring a custom storage volume.

For example, to set the size of your custom storage volume my-volume to 1 GiB, use the following command:

lxc storage volume set my-pool my-volume size=1GiB

To set the snapshot expiry time for your virtual machine my-vm to one month, use the following command:

lxc storage volume set my-pool virtual-machine/my-vm snapshots.expiry 1M

You can also edit the storage volume configuration by using the following command:

lxc storage volume edit <pool_name> [<volume_type>/]<volume_name>

Configure default values for storage volumes

You can define default volume configurations for a storage pool. To do so, set a storage pool configuration with a volume prefix, thus volume.<VOLUME_CONFIGURATION>=<VALUE>.

This value is then used for all new storage volumes in the pool, unless it is set explicitly for a volume or an instance. In general, the defaults set on a storage pool level (before the volume was created) can be overridden through the volume configuration, and the volume configuration can be overridden through the instance configuration (for storage volumes of type container or virtual-machine).

For example, to set a default volume size for a storage pool, use the following command:

lxc storage set [<remote>:]<pool_name> volume.size <value>

View storage volumes

You can display a list of all available storage volumes and check their configuration.

To list all available storage volumes, use the following command:

lxc storage volume list

To display the storage volumes for all projects (not only the default project), add the --all-projects flag.

You can also display the storage volumes in a specific storage pool by specifying the pool name:

lxc storage volume list <pool_name>

The resulting table contains, among other information, the storage volume type and the content type for each storage volume.

Note

Custom storage volumes might use the same name as instance volumes (for example, you might have a container named c1 with a container storage volume named c1 and a custom storage volume named c1). Therefore, to distinguish between instance storage volumes and custom storage volumes, all instance storage volumes must be referred to as <volume_type>/<volume_name> (for example, container/c1 or virtual-machine/vm) in commands.

To show detailed configuration information about a specific volume, use the following command:

lxc storage volume show <pool_name> [<volume_type>/]<volume_name>

To show state information about a specific volume, use the following command:

lxc storage volume info <pool_name> [<volume_type>/]<volume_name>

In both commands, the default storage volume type is custom, so you can leave out the <volume_type>/ when displaying information about a custom storage volume.

Resize a storage volume

If you need more storage in a volume, you can increase the size of your storage volume. In some cases, it is also possible to reduce the size of a storage volume.

To resize a storage volume, set its size configuration:

lxc storage volume set <pool_name> <volume_name> size <new_size>

Important

  • Growing a volume is possible if the storage pool has sufficient storage.

  • Shrinking a storage volume is only possible for storage volumes with content type filesystem. It is not guaranteed to work though, because you cannot shrink storage below its current used size.

  • Shrinking a storage volume with content type block is not possible.