Volumes

Volumes are used to store data.

Volumes are provisioned from storage pools and sit in a namespace. All volumes are thinly provisioned so only consume capacity which is actually used.

Volume names consist of lower case alphanumeric characters or ‘-‘, and must start and end with an alphanumeric character. By default, volumes are 5GB in size (overridden by --size) and formatted as ext4 (overridden by --fstype=ext2|ext3|ext4|xfs|btrfs).

In order to mount volumes into containers, they are formatted with a filesystem such as ext4. All volumes are accessible to any container anywhere on the cluster (global namespace) but each volume may only be mounted by one container at a time. Additional behaviours may be specified by adding labels.

Volumes can be created and managed using the standard Docker CLI or through the StorageOS CLI for more options and control.

Using the Docker CLI

The Docker CLI does not support namespaced volumes so all volumes created using the Docker CLI must be in the default namepsace.

To create a 15GB volume, run:

$ docker volume create --driver storageos --opt size=15 volume-name

To create a volume and provision to a Docker container in one step, run:

docker run --rm -ti --volume-driver storageos -v volume-name:/data alpine ash

When using dynamic provisioning it is not possible to specify options at creation time. The volume will default to 5GB, but the size can be dynamically expanded using the CLI or API.

To list all volume, run:

docker volume ls

Using the StorageOS CLI

With the StorageOS CLI, you must specify a namespace using the --namespace flag.

To create a 15GB volume in the default namespace, run:

$ storageos volume create --namespace default --size 15 --fstype ext4 volume-name
default/volume-name

To view all volumes in all namespaces, run:

$ storageos volume ls
NAMESPACE/NAME        SIZE                MOUNTED BY          MOUNTPOINT          STATUS              REPLICAS
default/volume-name   15GB                                                        active              0/0

To mount a volume on the current node into /mnt, run:

storageos volume mount default/volume-name /mnt

In order for the mount to succeed, StorageOS must be running on the node and the volume must not be mounted anywhere else. When the volume is mounted a lock is placed on the volume to ensure it is not written by multiple concurrent writers as this could lead to data inconsistency.

By default the volume will be formatted using ext4, which may be overridden or updated with --fstype.

Resizing volumes

To resize a volume, use storageos volume update --size <new_size_in_GB> default/volume-name.

The volume is expanded immediately but you will need to manually resize the filesystem by calling resize2fs.

Shrinking a volume is not supported.

Unmounting and removing volumes

To unmount a volume on the current node, run:

storageos volume unmount default/volume-name

The unmount command should be run on the node that has the volume mounted. Unmounting the volume detaches the filesystem from the node and removes the mount lock. In cases where the filesystem was unmounted manually using the Linux umount utility, or the node is no longer active, you can specify the --force flag to only remove the mount lock.

To delete a volume, run:

$ storageos volume rm default/volume-name
default/volume-name

All data in this volume will be lost.

This command will fail if the volume is mounted. To delete a mounted volume, add --force flag:

$ storageos volume rm --force default/volume-name
default/volume-name

Volumes may not be removed immediately as the data will be purged in the background.

Using node selector

A node selector is a constraint on where volumes may be deployed, based on node labels. For the volume to be eligible for a deployment on a node, selector must match node’s labels. An empty selector always matches a node.

If a group of nodes are labelled country=US, then a node selector can be used during volume creation:

$ storageos volume create --nodeSelector 'country=US'

Selectors may also be set-based:

country in (US, CA)
country notin (UK)

Since StorageOS selectors are similar to Kubernetes selectors, please check out documentation available there: https://kubernetes.io/docs/concepts/overview/working-with-objects/labels/#label-selectors.