[TechNotes] What Is LUN

Concepts

In a storage area network (SAN), a logical unit number (LUN) is used to identify a logical unit, which is a device addressed by SCSI. A storage system partitions physical disks into parts with logical addresses and allows hosts to access the parts. Such a partition is called a LUN. Generally, a LUN is a logical disk created on a SAN storage system.

How Does a Server Use LUNs? What Is a LUN on a Server?

A storage system can be connected to application servers running various operating systems (OSs), such as Windows, Linux, Unix (including AIX, HP-UX, and Solaris), and VMware. Figure 1-1 shows the process for application servers to use storage space.

Figure 1-1 Process for using storage space

1. The user creates LUNs on the storage system based on service requirements. For centralized management of LUNs, a LUN group must also be created and then mapped to a host group.

2. A host created on the storage system represents an application server. The user creates a host on the storage system and associates it with the application server. For centralized management of hosts, a host group must also be created.

3. The user creates a mapping view and adds the LUN group and host group to the mapping view. In this way, the application server, host group, and LUN group are logically associated.

4. After the storage system and application server are properly networked, the application server can scan LUNs to discover allocated storage space and read/write the LUNs.

LUN vs. Volume

The definitions of LUN and volume vary with vendors. This section is based on a general definition that considers volume as a server-side concept.

After a LUN is created on a storage system, it is a logical device on the storage system. When a server is connected to the storage system, it can identify the LUN on the storage system as a physical disk. The user can create one or more partitions on the physical disk to obtain one or more volumes. The volumes are logical devices on the server.

The following compares the capacity of volumes, partitions, and LUNs:

Volume = Partition ≤ Disk in the host's device manager = LUN ≤ Total capacity of disks on the storage device

LUN Masking vs. LUN Mapping

What Is LUN Masking?

LUN masking: A LUN is bound to the World Wide Port Name (WWPN) or iSCSI Qualified Name (IQN) of a host port to set up a one-to-one or many-to-one connection and access relationship between the LUN and the host port. The host can identify the same LUN regardless of which port on the storage system the host connects to.

What Is LUN Mapping?

LUN mapping: A LUN is bound to a front-end port of a storage system. Hosts can access different LUNs when they connect to different front-end ports.

Use of LUN Masking and LUN Mapping on Huawei Storage

After a host group and a LUN group are added to a mapping view, the application server, host group, and LUN group are logically associated. Adding the host group to the mapping view implement LUN masking. In addition, you can add a port group to the mapping view to implement LUN mapping. The LUNs in the LUN group and the hosts in the host group use the ports in the port group for communication. If LUN mapping is not implemented, the LUNs and hosts use randomly allocated ports for communication.

How Do I Create a LUN?

For details on how to create LUNs on Huawei storage systems, see the following:

• Creating a LUN on OceanStor V3 Series V300R006

• Creating a LUN on OceanStor V5 Series V500R007

• Creating a LUN on OceanStor Dorado V3 Series V300R002

How Do I Expand LUN Capacity?

Figure 1-2 shows the expansion process.

Figure 1-2 Capacity expansion process

Table 1-1 describes each step in detail.

Table 1-1 Steps for expanding LUN capacity

For details on how to expand LUN capacity on Huawei storage systems, see the following:

• Expanding LUN Capacity on OceanStor V3 Series V300R006

• Expanding LUN Capacity on OceanStor V5 Series V500R007

• Expanding LUN Capacity on OceanStor Dorado V3 Series V300R002