Understanding Cisco Cloud Fundamentals Objective 5.3

Describe basic SAN storage concepts

Initiator

An application or production system end-point (a server) that is capable of initiating a SCSI session, sending SCSI commands and I/O requests. Initiators are also identified by unique addressing methods.

Target

A storage system end-point that provides a service of processing SCSI commands and I/O requests from an initiator. A target is created by the storage system’s administrator, and is identified by unique addressing methods. A target, once configured, consists of zero or more logical units

Zoning

Zones are the basic form of data path security in a Fibre Channel environment. Zones are used to define which end devices (two or more) in a fabric can communicate with each other. Zones are grouped together into zone sets. For the zones to be active, the zone set to which the zones belong needs to be activated. Individual zone members can be part of multiple zones. Zones can be part of multiple zone sets. Multiple zone sets can be defined in a fabric. At any given time, only one zone set can be active.

If zoning is not activated in a fabric, all the end devices are part of the default zone. If zoning is activated, any end devices that are not part of an active zone are part of the default zone. The default zone policy is set either to deny (none of the end devices that are part of the default zone can communicate with each other) or permit (all the devices that are part of the default zone can communicate with each other).

VSAN

A virtual SAN (VSAN) is a logical grouping of ports in a single switch or across multiple switches that function like a single fabric. A VSAN is isolated from other VSANs in terms of traffic, security, and fabric services. Because of this, changes made to one VSAN do not affect the remaining VSANs, even though they may be present in the same physical SAN infrastructure hardware. Using VSANs, multiple logical SANs can be hosted on a physical SAN hardware infrastructure. A VSAN lends itself to SAN island consolidation on a higher port density physical switch, along with traffic isolation and increased security. Once a VSAN is created, it has all the properties and functions of a SAN.

Multiple VSANs can be defined on a physical switch. Each VSAN will require it own domain_ID. A single VSAN can span 239 physical switches (a Fibre Channel standards limit). At the current time, a maximum of 256 VSANs are supported in a physical switch.

Using VSANs provides some important advantages:

• VSAN traffic stays within the VSAN boundaries. Devices can be part of just one VSAN.
• VSANs allow you to create multiple logical SAN instances on top of a physical SAN infrastructure. This allows for the consolidation of multiple SAN islands onto a physical infrastructure, which minimizes the hardware that needs to be managed.
• Each VSAN has it own set of fabric services, which allows the SAN infrastructure to be scalable and highly available.
• Additional SAN infrastructure resources such as VSAN ports can be added and changed as needed without impacting VSAN ports that are already a part of the SAN infrastructure. Moving ports between VSANs is as simple as assigning the port to a different VSAN.

VSANs are numbered from 1 through 4094. VSAN 1 and VSAN 4094 are predefined and have very specific roles. The user-specified VSAN range is from 2 through 4093. VSAN 1 is the default VSAN that contains all ports by default. VSAN 1 is used as a management VSAN. VSAN 4094 is the isolated VSAN into which all orphaned ports are assigned. Devices that are part of VSAN 4094 cannot communicate with each other.

LUN

A LUN is a logical reference to a portion of a storage subsystem. A LUN can comprise a disk, a section of a disk, a whole disk array, or a section of a disk array in the subsystem. This logical reference, when it is assigned to a server in your SAN, acts as a physical disk drive that the server can read and write to. Using LUNs simplifies the management of storage resources in your SAN, because they serve as logical identifiers through which you can assign access and control privileges.

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