# Local Disk Manager

Local Disk Manager (LDM) is one of the modules of HwameiStor. `LDM` is used to simplify the management of disks on nodes. It can abstract the disk on a node into a resource for monitoring and management purposes. It's a daemon that will be deployed on each node, then detect the disk on the node, abstract it into local disk (LD) resources and save it to kubernetes.

![LDM architecture](https://docs.daocloud.io/daocloud-docs-images/docs/en/docs/storage/hwameistor/img/ldm-en.png)

At present, the LDM project is still in the `alpha` stage.

## Concepts

LocalDisk (LD): LDM abstracts disk resources into objects in kubernetes. An `LD` resource object represents the disk resources on the host.

LocalDiskClaim (LDC): This is a way to use disks. A user can add the disk description to select a disk for use.

!!! note

    At present, LDC supports the following options to describe disk:

    - NodeName
    - Capacity
    - DiskType (such as HDD/SSD/NVMe)

## Usage

1. Get the LocalDisk information.

    ```bash
    kubectl get localdisk
    NAME               NODEMATCH        PHASE
    10-6-118-11-sda    10-6-118-11      Available
    10-6-118-11-sdb    10-6-118-11      Available
    ```

    Get locally discovered disk resource information with three columns displayed.

    - **NAME:** represents how this disk is displayed in the cluster resources.
    - **NODEMATCH:** indicates which host this disk is on.
    - **PHASE:** represents the current state of the disk.

    Use `kubectl get localdisk <name> -o yaml` to view more information about disks.

2. Claim available disks.

    1. Apply a LocalDiskClaim.

        ```bash
        cat << EOF | kubectl apply -f -
        apiVersion: hwameistor.io/v1alpha1
        kind: LocalDiskClaim
        metadata:
          name: <localDiskClaimName>
        spec:
          description:
            # e.g. HDD,SSD,NVMe
            diskType: <diskType>
          # the node where disks attached
          nodeName: <nodeName>
          # the owner of the allocated disks e.g. local-storage,local-disk-manager
          owner: <ownerName>
        EOF
        ```

        Allocate available disks by issuing a disk usage request. In the request description, you can add more requirements about the disk, such as disk type and capacity.

    2. Get the LocalDiskClaim information.

        ```bash
        kubectl get localdiskclaim <name>
        ```

    3. Once the LDC is processed successfully, it will be cleanup by the system automatically. The result will be recorded in the `LocalStorageNode` if the owner is `local-storage`.