About LVM thin volumes

To enable advanced storage capabilities, such as volume snapshots and volume cloning, complete specific configuration steps. Preparing your environment ensures that the necessary components are active and ready to support these features for your workloads.

The following list describes the configuration steps:

  • Configure both the logical volume manager storage (LVMS) provider and the node.

  • Provision a logical volume manager (LVM) thin-pool on the RHEL for Edge host.

  • Attach LVM thin-pools to a volume group.

Important

To create Container Storage Interface (CSI) snapshots, you must configure thin volumes on the RHEL for Edge host. The CSI does not support volume shrinking.
Important

When using thin provisioning, you must monitor the storage pool and add more capacity as the available physical space runs out. You can configure the storage pool to auto expand when there is available space within the volume group (VG). See "Creating a thin logical volume".

For LVMS to manage thin logical volumes (LVs), a thin-pool device-class array must be specified in the etc/lvmd.yaml configuration file. Multiple thin-pool device classes are permitted.

If additional storage pools are configured with device classes, then additional storage classes must also exist to expose the storage pools to users and workloads. To enable dynamic provisioning on a thin-pool, a StorageClass resource must be present on the node. The StorageClass resource specifies the source device-class array in the topolvm.io/device-class parameter.

Example lvmd.yaml file that specifies a single device class for a thin-pool
socket-name:
device-classes:
  - name: thin
    default: true
    spare-gb: 0
    thin-pool:
      name: thin
      overprovision-ratio: 1
    type: thin
    volume-group: ssd

where:

socket-name

Specifies the UNIX domain socket endpoint of gRPC. Defaults to /run/lvmd/lvmd.socket. Takes a string value.

device-classes

Specifies a list of maps for the settings for each device-class.

device-classes.name

Specifies the unique name of the device-class. Takes a string value.

device-classes.spare-gb

Specifies storage capacity in GB to be left unallocated in the volume group. Defaults to 0. Takes an unsigned 64-bit integer.

thin-pool.overprovision-ratio

Specifies a float factor by which you can provision additional storage based on the available storage in the thin pool. For example, if this field is set to 10, you can provision up to 10 times the amount of available storage in the thin pool. To disable over-provisioning, set this field to 1.

type

Specifies thin provisioning is required to create volume snapshots.

volume-group

Specifies the group where the device-class creates the logical volumes. Takes a string value.

Important

When multiple PVCs are created simultaneously, a race condition prevents LVMS from accurately tracking the allocated space and preserving the storage capacity for a device class. Use separate volume groups and device classes to protect the storage of highly dynamic workloads from each other.

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