How to add 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 a custom storage volume#

Use the following command to create a custom storage volume 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.

Attach a custom storage 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 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.

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>

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.