vSAN introduces specific terms and definitions that are important to understand. Before you get start designing your vSAN network, review the key vSAN networking terms and definitions.

CLOM

The Cluster-Level Object Manager (CLOM) is responsible for ensuring that an object's configuration matches its storage policy. The CLOM checks whether enough disk groups are available to satisfy that policy. It decides where to place components and witnesses in a cluster.

CMMDS

The Cluster Monitoring, Membership, and Directory Service (CMMDS) is responsible for the recovery and maintenance of a cluster of networked node members. It manages the inventory of items such as host nodes, devices, and networks. It also stores metadata information, such as policies and RAID configuration for vSAN objects.

DOM

The Distributed Object Manager (DOM) is responsible for creating the components and distributing them across the cluster. After a DOM object is created, one of the nodes (host) is nominated as the DOM owner for that object. This host handles all IOPS to that DOM object by locating the respective child components across the cluster and redirecting the I/O to respective components over the vSAN network. DOM objects include vdisk, snapshot, vmnamespace, vmswap, vmem, and so on.

LSOM

The Log-Structured Object Manager (LSOM) is responsible for locally storing the data on the vSAN file system as vSAN Component or LSOM-Object (data component or witness component).

NIC Teaming

Network Interface Card (NIC) teaming can be defined as two or more network adapters (NICs) that are set up as a "team" for high availability and load balancing.

NIOC

Network I/O Control (NIOC) determines the bandwidth that different network traffic types are given on a vSphere distributed switch. The bandwidth distribution is a user configurable parameter. When NIOC is enabled, distributed switch traffic is divided into predefined network resource pools: Fault Tolerance traffic, iSCSI traffic, vMotion traffic, management traffic, vSphere Replication traffic, NFS traffic, and virtual machine traffic.

Objects and Components

Each object is composed of a set of components, determined by capabilities that are in use in the VM Storage Policy.

A vSAN datastore contains several object types.

VM Home Namespace
The VM Home Namespace is a virtual machine home directory where all virtual machine configuration files are stored. This includes files such as .vmx, log files, vmdks, and snapshot delta description files.
VMDK
VMDK is a virtual machine disk or .vmdk file that stores the contents of the virtual machine's hard disk drive.
VM Swap Object
VM Swap Objects are created when a virtual machine is powered on.
Snapshot Delta VMDKs
Snapshot Delta VMDKs are created when virtual machine snapshots are taken.
Memory Object
Memory Objects are created when the snapshot memory option is selected when creating or suspending a virtual machine.

RDT

The Reliable Data Transport (RDT) protocol is used for communication between hosts over the vSAN VMkernel ports. It uses TCP at the transport layer and is responsible to create and destroy TCP connections (sockets) on demand. It is optimized to send large files.

SPBM

Storage Policy-Based Management (SPBM) provides a storage policy framework that serves as a single unified control panel across a broad range of data services and storage solutions. This framework helps you to align storage with application demands of your virtual machines.

VASA

The vSphere Storage APIs for Storage Awareness (VASA) is a set of application program interfaces (APIs) that enables vCenter Server to recognize the capabilities of storage arrays. VASA providers communicate with vCenter Server to determine the storage topology, capability, and state information which supports policy-based management, operations management, and DRS functionality.

VLAN

A VLAN enables a single physical LAN segment to be further segmented so that groups of ports are isolated from one another as if they were on physically different segments.

Witness Component

A witness is a component that contains only metadata and does not contain any actual application data. It serves as a tiebreaker when a decision must be made regarding the availability of the surviving datastore components, after a potential failure. A witness consumes approximately 2 MB of space for metadata on the vSAN datastore when using on-disk format 1.0, and 4 MB for the on-disk format for version 2.0 and later.