Storage Class Parameters

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.

The setting is supported only when using "nvmf" protocol.

"local"

A flag of the type Boolean, with the default value of true. The flag controls the scheduling behaviour of nexus and replicas to storage nodes in the cluster.

All the following values are interpreted as "true" and anything else as "false": 'y', 'Y', 'yes', 'Yes', 'YES', 'true', 'True', 'TRUE', 'on', 'On', 'ON'.

This value must be set to true for correct operation of Mayastor provisioning and publishing. It is recommended that the volumeBindingMode in storage class be set to WaitForFirstConsumer. This limitation will be removed in a future release

A consequence of the above limitation is that applications pods which use Mayastor provisioned PVs may only be scheduled on nodes which are running Mayastor pods (i.e. data engine container). That is to say, only on MSNs. This limitaion will be removed in a future release.

"protocol"

Supported values are "nvmf" and "iscsi". It is the protocol that is used for mounting the volume (target) on the application node. Not to be confused with the protocol that is used between nexus and replicas, that is always "nvmf". By "nvmf" here, we mean NVMe over TCP protocol - the next generation protocol that is supposed to replace iSCSI. We definitely recommend to use "nvmf". "iscsi" is not full-featured and provided only for users running older kernels that do not support NVMe over TCP yet but still would like to give Mayastor a try.

"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.