SAN Architecture

This document will be using the EMC symmetrix configuration. There are a number of EMC Symmetrix configurations but they all use the same architecture as detailed below.

Front End Director Ports (SA-16b:1)
Front End Director (SA-16b)
Back End Director (DA-02b)
Back End Director Ports (DA-02b:c)
Disk Devices

Front End Director
A channel director (front end director) is a card that connects a host to the symmetrix, each card can have upto four ports.

Symmetrix cache memory buffers I/O transfers between the director channels and the storage devices. The cache is divided up into regions to eliminate contension.

Back End Director
A disk director (back end director) transfers data from disk to cache. Each back-end director can have upto four interfaces (C,D,E and F). Each back-end director interface can handle seven SCSI ids (0-6)

Disk Devices
The disk devices that are attached to the back-end directors could be either SCSI or FC-AL.

The direct matrix interconnect is a matrix of high speed connections to all componentswith bandwidth up to 64Gb/s

SAN Components

The are many components to a SAN Architecture. A host can connect to a SAN via direct connection or via a SAN switch.

Host HBA Host bus adaptor cards are used to access SAN storage systems
SAN Cables

There are many types of cables and connectors:

Types: Multimode (<500m), single mode (>500m) and copper
Connectors: ST, SC (1Gb), LC (2Gb)

SAN Switches

The primary function of a switch is to provide a physical connection and logical routing of data frames between the attached devices.

Support multiple protocols: Fibre channel, iSCSI, FCIP, iFCP
Type of switch: Workgroup, Directors

SAN Zoning

Zoning is used to partition a fibre channel switched fabric into subsets of logical devices. Each zone contains a set of members that are permitted to access each other. Members are HBA's, switch ports and SAN ports.

Types of zoning: hard, soft and mixed

Zone set s This is a group of zones that relate to one another, only one zone set can be active at any one time.
Storage arrays Storage array is were all the disk devices are located.
Volume access control This is also know as LUN masking. The storage array maintains a database that contains a map of the storage volumes and WWN's that are allowed to access it. The VCM database in a symmetrix would contain the LUN masking information.

SAN Login

The below table documents the various proccesses that occur when a fibre channel device is connected to a SAN

Information/process FLOGI (fabric login) PLOGI (port login) PRLI (process login)
What is need ? - Link initialization
- Cable
- HBA and driver
- Switch Port
- Zoning
- Persistent binding
- Driver setting
- Device masking (target)
- Device mapping (initiator)
- Driver setting (initiator)
What information is passed

- S_ID
- Protocol
- Class
- Zoning

- S_ID
- Class
- BB Credit
Who does the communication ? - N_port to F_port - N_port to N_port - ULP( scsi-3 to scsi-3)
where to find the information ?

- syslog
- switch utilites

- Event viewer
- Switch viewer

- Syslog
- Driver Ulitities

- Driver utilities

- Syslog
- Host based volume management

- Driver Utilities
- Host based volume management
- Device Manager

If any one of the above were to fail then the host will not be allowed to access the disks on the SAN.

VCM Database

The Symmetrix Volume Configuration Management (VCM) database stores access configurations that are used to grant host access to logical devices in a Symmetrix storage array.

The VCM database resides on a special system resource logical device, referred to as the VCMDB device, on each Symmetrix storage array.

Information stored in the VCM database includes, but is not limited to:

Masking operations performed on Symmetrix storage devices result in modifications to the VCM database in the Symmetrix array. The VCM database can be backed up, restored, initialized and activated. The Symmetrix SDM Agent must be running in order to perform VCM database operations (except deleting backup files).


There are three models of switchs M-series (Mcdata), B-series (Brocade) and the MDS-series (Cisco). Each of the switch offer a web interface and a CLI. The following tasks can be set on most switches:

BB Credit Configure the number of buffers that are available to attached devices for frame receipt default 16. Values range 1-16.
R_A_TOV Resource allocation time out value. This works with the E_D_TOV to determine switch actions when presented with an error condition
E_D_TOV Error detect time out value. This timer is used to flag potential error condition when an expected response is not received within the set time

The CLI commands can be viewed here for all switches, also a detailed view of zoning can be located here.

Host HBA's

The table below outlines which card will work with a particular O/S

Solaris Emulex PCI (lputil)
HPUX PCI-X gigabit fibre channel and ethernet card
AIX FC6227/6228/6239 using IBM native drivers
Windows Emulex (HBAnyware or lputilnt)
Linux Emulex PCI (lputil)

The card configuration page can been seen here

Clariion configuration

The Clariion cheat sheet can be seen from this link

Symmetrix configuration

The Symmetrix cheat sheet can be seen from this link.