By default, on the host will be used for storing the volume data. You can avoid using the default directory by adding a new disk, then disable scheduling for /var/lib/longhorn.

To add a new disk for a node, head to the Node tab, select one of the nodes, and select Edit Disks in the dropdown menu.

To add any additional disks, you need to:

1. Add the path of the mounted disk into the disk list of the node.

Longhorn will detect the storage information (e.g. maximum space, available space) about the disk automatically, and start scheduling to it if it’s possible to accommodate the volume. A path mounted by the existing disk won’t be allowed.

The kubelet needs to preserve node stability when available compute resources are low. This is especially important when dealing with incompressible compute resources, such as memory or disk space. If such resources are exhausted, nodes become unstable. To avoid kubelet Disk pressure issue after scheduling several volumes, by default, Longhorn reserved 30% of root disk space () to ensure node stability.

If you don’t want to use the original mount path of a disk on the node, you can use mount --bind to create an alternative/alias path for the disk, then use it with Longhorn. Notice that soft link ln -s won’t work since it will not get populated correctly inside the pod.

Longhorn will identify the disk using the path, so the users need to make sure the alternative path are correctly mounted when the node reboots, e.g. by adding it to fstab.

In order to remove a disk, two conditions need to be met:

• The scheduling for the disk must be disabled
• There is no existing replica using the disk, including any replicas in an error state.

Once those two conditions are met, you should be allowed to remove the disk.

There are two global settings affect the scheduling of the volume.

• StorageMinimalAvailablePercentage defines when a disk cannot be scheduled with more volumes. The default value is 10 (%). The bigger value between MaximumStorage * StorageMinimalAvailablePercentage / 100 and MaximumStorage - ReservedStorage will be used to determine if a disk is running low and cannot be scheduled with more volumes.

Notice that currently there is no guarantee that the space volumes use won’t exceed the StorageMinimalAvailablePercentage, because:

1. Longhorn volumes can be bigger than the specified size, due to fact that the snapshot contains the old state of the volume.
2. Longhorn does over-provisioning by default.