Storage class resource in Kubernetes is used to supply parameters to volumes when they are created. It is a convenient way of grouping volumes with common characteristics. All parameters take a string value. Brief explanation of each supported Mayastor parameter follows.

"fsType"

File system that will be used when mounting the volume. The default file system when not specified is 'ext4'. We recommend to use 'xfs' that is considered to be more advanced and performant. Though make sure that XFS is installed on all nodes in the cluster before using it.

"ioTimeout"

Expressed in seconds and it sets the io_timeout parameter in the linux block device driver for Mayastor volume. It also sets ctrl-loss-tmo timeout in linux NVMe driver that is used for detecting inaccessible target (nexus in our case). In either case, if IO cannot be served by Mayastor volume, because it is stuck or because the nvmf target is not there, it will take roughly this time to the initiator to return an error to data consumer, which can be either filesystem or an application if using raw block volume. The usual reaction of a filesystem to such error is to switch the filesystem to read-only state and require manual intervention from user - remounting. Be careful when setting this to a low value because any node reboot that does not fit into this time interval may require manual intervention afterwards or can result in application failure - depending on how the error is handled by the application.

"protocol"

The parameter 'protocol' takes the value nvmf(NVMe over TCP protocol). It is used to mount the volume (target) on the application node.

"repl"

The string value should be a number and the number should be greater than zero. Mayastor control plane will try to keep always this many copies of the data if possible. If set to one then the volume does not tolerate any node failure. If set to two, then it tolerates one node failure. If set to three, then two node failures, etc.

Create DiskPool(s)

What is a DiskPool?

When a node allocates storage capacity for a replica of a persistent volume (PV) it does so from a DiskPool. Each node may create and manage zero, one, or more such pools. The ownership of a pool by a node is exclusive. A pool can manage only one block device, which constitutes the entire data persistence layer for that pool and thus defines its maximum storage capacity.

A pool is defined declaratively, through the creation of a corresponding DiskPool custom resource on the cluster. The DiskPool must be created in the same namespace where Mayastor has been deployed. User configurable parameters of this resource type include a unique name for the pool, the node name on which it will be hosted and a reference to a disk device which is accessible from that node. The pool definition requires the reference to its member block device to adhere to a discrete range of schemas, each associated with a specific access mechanism/transport/ or device type.

:::note Mayastor versions before 2.0.1 had an upper limit on the number of retry attempts in the case of failure in create events in the DSP operator. With this release, the upper limit has been removed, which ensures that the DiskPool operator indefinitely reconciles with the CR. :::

Permissible Schemes for spec.disks under DiskPool CR

Once a node has created a pool it is assumed that it henceforth has exclusive use of the associated block device; it should not be partitioned, formatted, or shared with another application or process. Any pre-existing data on the device will be destroyed.

Configure Pools for Use with this Quickstart

To get started, it is necessary to create and host at least one pool on one of the nodes in the cluster. The number of pools available limits the extent to which the synchronous N-way mirroring (replication) of PVs can be configured; the number of pools configured should be equal to or greater than the desired maximum replication factor of the PVs to be created. Also, while placing data replicas ensure that appropriate redundancy is provided. Mayastor's control plane will avoid placing more than one replica of a volume on the same node. For example, the minimum viable configuration for a Mayastor deployment which is intended to implement 3-way mirrored PVs must have three nodes, each having one DiskPool, with each of those pools having one unique block device allocated to it.

Using one or more the following examples as templates, create the required type and number of pools.

cat <<EOF | kubectl create -f -
apiVersion: "openebs.io/v1alpha1"
kind: DiskPool
metadata:
  name: pool-on-node-1
  namespace: mayastor
spec:
  node: workernode-1-hostname
  disks: ["/dev/disk/by-uuid/<uuid>"]
EOF

apiVersion: "openebs.io/v1alpha1"
kind: DiskPool
metadata:
  name: INSERT_POOL_NAME_HERE
  namespace: mayastor
spec:
  node: INSERT_WORKERNODE_HOSTNAME_HERE
  disks: ["INSERT_DEVICE_URI_HERE"]

Verify Pool Creation and Status

The status of DiskPools may be determined by reference to their cluster CRs. Available, healthy pools should report their State as online. Verify that the expected number of pools have been created and that they are online.

kubectl get dsp -n mayastor

NAME             NODE          STATE    POOL_STATUS   CAPACITY      USED   AVAILABLE
pool-on-node-1   node-1-14944  Online   Online        10724835328   0      10724835328
pool-on-node-2   node-2-14944  Online   Online        10724835328   0      10724835328
pool-on-node-3   node-3-14944  Online   Online        10724835328   0      10724835328

Pool configuration and state information can also be obtained by using the Mayastor kubectl plugin

Create Mayastor StorageClass(s)

Mayastor dynamically provisions PersistentVolumes (PVs) based on StorageClass definitions created by the user. Parameters of the definition are used to set the characteristics and behaviour of its associated PVs. For a detailed description of these parameters see storage class parameter description. Most importantly StorageClass definition is used to control the level of data protection afforded to it (that is, the number of synchronous data replicas which are maintained, for purposes of redundancy). It is possible to create any number of StorageClass definitions, spanning all permitted parameter permutations.

We illustrate this quickstart guide with two examples of possible use cases; one which offers no data redundancy (i.e. a single data replica), and another having three data replicas. You can modify these as required to match your own desired test cases, within the limitations of the cluster under test.

cat <<EOF | kubectl create -f -
apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: mayastor-1
parameters:
  ioTimeout: "30"
  protocol: nvmf
  repl: "1"
provisioner: io.openebs.csi-mayastor
EOF

cat <<EOF | kubectl create -f -
apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: mayastor-3
parameters:
  ioTimeout: "30"
  protocol: nvmf
  repl: "3"
provisioner: io.openebs.csi-mayastor
EOF