Storage Area Network (SAN) Basics

SAN:Storage Area Network – It interconnects different types of storage devices (such as disk arrays, Tape drives) with the servers, as if storage devices are locally attached to the servers.
Access - Block Level

NAS:Network Attached Storage – It is a file-level computer data storage connected to a network providing data access to heterogeneous clients.
Access - File Level

DAS:Direct Attached Storage – A storage device directly attached to the server without the storage network.
Access - Block Level

Redundant Array of Independent Disks (RAID):Redundant – An extra “COPY” of data
Array – Number of disks together

Note: Parity is calculated using Exclusive OR (XOR).

Hardware Raid Vs Software Raid:



LUN: Logical Unit Number – Unique identification number of a SCSI device logical unit.

Zoning:Process that partitioning fabric (switch) into smaller groups for adding security.
Each hosts connected to the SAN should have the allowed access to controlled subset of LUNs.

Port Zoning:It uses physical ports to define security zones.

WWN Zoning:It uses name server in the switch to either allow or block based on the WWN.

Lun Masking:Process that makes LUN available to some hosts and unavailable to other hosts.

FC SAN Topologies:
Point to Point:It is the simplest topology which allows the host and storage connect directly.

Arbitrated Loop:· Devices are connected in a one way loop fashion in a ring topology.
· One node acts as a transmitter and next node acts as a receiver.
· A maximum supported storage device is 127.

Switched Fabric:Storage devices are connected to each other via switches.

WWN:8 byte(64 bit) number. Hardcoded into a fibre channel HBA, used for identifying individual port in fabric.
First 3 bytes number purchased from IEEE OUI(Organizationally Unique Identifier) and the rest supplied by the vendor.

WWNN and WWPN:WWPN -> Assigned to Port
WWNN -> Assigned to Node (endpoint or device). Different WWPN can have the same WWNN on the network.

Multipath:In a SAN environment, each LUNs are accessed through multiple paths, as the storage controller and HBA having multiple ports.