LUN Volume

• Volumes contain file systems in a NAS environment and LUNs in a SAN environment.

A LUN (logical unit number) is an identifier for a device called a logical unit addressed by a SAN protocol.
LUNs are the basic unit of storage in a SAN configuration
The Windows host sees LUNs on your storage system as virtual disks.
You can nondisruptively move LUNs to different volumes as needed.
https://docs.netapp.com/ontap-9/index.jsp?topic=%2Fcom.netapp.doc.dot-cm-concepts%2FGUID-372DCFC1-3C68-408F-B404-E26514BEB8F7.html

Volumes contain file systems in a NAS environment and LUNs in a SAN environment.
A LUN (logical unit number) is an identifier for a device called a logical unit addressed by a SAN protocol.
LUNs are the basic unit of storage in a SAN configuration
The Windows host sees LUNs on your storage system as virtual disks.
You can nondisruptively move LUNs to different volumes as needed.
https://docs.netapp.com/ontap-9/index.jsp?topic=%2Fcom.netapp.doc.dot-cm-concepts%2FGUID-372DCFC1-3C68-408F-B404-E26514BEB8F7.html

• you have the computer (also called a “host,” “initiator,” or even just “CPU” sometimes.

you have the physical media (also called a “target,” “drive,” “HDD,” or “SSD,” etc.).
Hosts need Volumes, so those volumes have to be made up of something that eventually sits on a real, physical drive (whether it be spinning drives or SSDs, etc.).
From the storage’s perspective, the physical media is broken down from a physical entity (the actual drive), into a logical entity, and given a number (hence the “Logical Unit Number”, or LUN).
In between there is a very important piece of software that makes a translation between that LUN and what the host can see as a Volume, called the Volume Manager.
https://jmetz.com/2016/11/whats-the-difference-between-a-lun-and-a-volume/

• In computer storage, a logical unit number, or LUN, is a number used to identify a logical unit, which is a device addressed by the SCSI protocol or Storage Area Network protocols which encapsulate SCSI, such as Fibre Channel or iSCSI.

A LUN may be used with any device which supports read/write operations, such as a tape drive, but is most often used to refer to a logical disk as created on a SAN.
https://en.wikipedia.org/wiki/Logical_unit_number

• What is a LUN (Logical Unit Number)?

A logical unit number (LUN) is an identifier used for labeling and designating subsystems of physical or virtual storage. Depending on the environment, a LUN may refer to a subsection of a disk or a disk in its entirety. Different areas in physical drives are assigned LUNs so data can be read, written or fetched correctly from servers on a storage area network (SAN). In both hard disk drives (HDDs) and solid state drives (SSDs), volumes of LUNs make up the physical drive.
What a LUN is and what a LUN can do
A LUN can represent one disk, an entire redundant array of independent disks (RAID), or partitions of a disk, all of which execute I/O commands. LUNs allow users to differentiate between and manage separate shared volumes on a single SAN. They are the identifiers for building blocks of information on a physical disk drive and in some cases, virtual drives or virtual machines (VMs). LUNs are used to label slices of disk storage that are viewable from a server. They can also function as partitions, sectioning off portions of a volume from one another. They separate portions of disks that use different operating systems or have unique application requirements. Today, virtual or “thin” LUNs are provisioned on virtual disks, representing virtual storage with no association to storage on any physical drive, disk or device
Different types of LUNs
A simple LUN is the basic building block upon which other types are based. A simple LUN represents one portion of one disk or one physical disk in its entirety—that's it. On the other hand, some LUNs are larger than one physical disk, so they “span” across two or more physical disks; these are called spanned LUNs.
Mirrored LUNs do use two physical disks but only for mirroring the information and data held within one of the disks.
The striped LUN also uses two or more disks in the same way as a spanned LUN
Striped LUNs with parity offer the same convenience as the striped LUN with the safety of backup data (parity) written to physical disks simultaneously.
https://www.tintri.com/faqs/what-is-a-lun-logical-unit-number