Discovery-Client Command

The NVMe-over-Fabrics specification defines the concept of a discovery controller that an NVMe host can query on a fabric network to discover NVMe subsystems. These subsystems are contained in NVMe targets that can be connected from the network.

Note that the base NVMe specification defines the NQN (NVMe Qualified Name) format, which an NVMe endpoint (device, subsystem, etc) must follow to guarantee a unique name under the NVMe standard. In particular, the host NQN uniquely identifies the NVMe host, and can be used by the discovery controller to control what NVMe target resources are allocated to the NVMe host for a connection.

Install the discovery-client rpm

yum install -y discovery-client

Start the discovery-client service

systemctl start discovery-client.service

Get the hostnqn

cat /etc/nvme/hostnqn

In case there is no hostnqn, you can generate one by using the following command:

nvme gen-hostnqn > /etc/nvme/hostnqn

The simplified syntax of this command is:

discovery-client connect-all -t tcp -a <ip> -s 8009 -q <hostnqn> -p

These are only a small sample of the possible parameters. See the discovery-client help menu for a complete list and usage of the discovery-client command. We have chosen these parameters as an example of the minimum required to connect to and use an NVMe/TCP volume.

After the application client connects to the Lightbits storage cluster, the volumes that this application client can access appear as local block devices. The following example shows how to use the Linux nvmecommand to list all block devices after the connectcommand finishes.

Sample Command

$ nvme list

Sample Output

Node             SN                   Model                                    Namespace Usage                      Format           FW Rev  

---------------- -------------------- ---------------------------------------- --------- -------------------------- ---------------- --------

/dev/nvme11n1    f2e1b3930c2ed3       LightBox                                 1           4.29  GB /   4.29  GB      4 KiB +  0 B   1.0

/dev/nvme11n2    f2e1b3930c2ed3       LightBox                                 3           4.29  GB /   4.29  GB      4 KiB +  0 B   1.0

/dev/nvme11n3    f2e1b3930c2ed3       LightBox                                 4          12.88  GB /  12.88  GB      4 KiB +  0 B   1.0

/dev/nvme11n4    f2e1b3930c2ed3       LightBox                                 5          12.88  GB /  12.88  GB      4 KiB +  0 B   1.0

In this example, the Lightbits storage server serves four volumes via NVMe/TCP. These volumes are mapped to the /dev Linux file system path. The NVMe/TCP block device names are listed in the Node column.