SAN Design: March 29, 2001 3:18 pm
53-0001575-01 BROCADE Technical Note Page: 25 of 31
of Fibre Channel is that data is transferred based on buffer credits assigned to ports and sending and receiving devices manage the credits so
that there is never an overrun of data in the switch.
Blocking is also called over-subscription -- where multiple initiator ports are limited by ISL links or paths in the fabric and, for example, 3
devices must share a single link between switches [a switch with 12 N-port nodes and 4 ISLs is 3:1 over-subscription]. An ideal non-block-
ing design has a subscription ratio of 1:1. However many devices do not have a bandwidth that can saturate a Fibre Channel data path and
allowing multiple devices to share a data path given the bursty nature of much data traffic can still result in high performance with limited
blocking. Knowing your devices and the nature of your data usage is key to implementing a SAN design with good performance.
3.8 SAN MANAGEMENT
The SilkWorm switch supports a number of management interfaces. These are:
•Telnet. A telnet session can be established with the switch that supports a command line interface. An administrator can login and
execute a number of commands that allow for showing switch status, port status, temperature and fan status, and for configuring
switch parameters. When BROCADE ZONING is licensed, a command line interface allows for defining fabric level zone
configurations.
•SNMP. Per the Fibre Channel FC-GS specifications, the SilkWorm switch supports a Fabric Element MIB and a BROCADE specific
MIB. Traps are defined for switch events and SNMP management software can be alerted to trap events. Similarly management
software can access switch information available via the telnet session.
•BROCADE WEB TOOLS. BROCADE supplies a licensed software option that allows Netscape or Internet Explorer browsers to
interact with an HTML server in the switch. A graphical view of all switches in the fabric is displayed and individual switch can be
selected for further drill down on switch/port information and for switch setup and configuration. Some OEMs have provided hooks
into SNMP management tools or custom disk management tools the invocation of web tools when switch management is required.
•SES (SCSI Enclosure Services). This is a programmatic interface within the switch that can be invoked from SCSI protocol as
defined in the SES specification. It allows for switch management via a host bus adapter that supports the SCSI FCA protocol. It
can be used when a separate out-of-band management tool is not desirable and when other device management is being conducted
via SES.
•Front Panel. The SilkWorm 2800 switch model (and 1600) feature a front key panel and display that supports most (but not all) telnet
commands. Basic switch addresses can be set, status information viewed, and configuration parameters set using the front panel.
With the large variety of management interfaces it is possible to accommodate a wide variety of SAN management approaches. The first
consideration should be decide if in-band (using FC protocol such as SES or using an HBA that supports IP over FC) or out-of-band man-
agement is preferred. Out-of-band would use the switch Ethernet port for connection to the fabric. It should be noted that the SilkWorm fab-
ric supports the ability to connect to one switch in the fabric via the switch Ethernet port, and to then connect to all other switches in the
Definition: ISL subscription is the ratio of input ports which might want to cross between
switches to the number of ISLs over which the traffic could cross. Over subscription occurs
when the ration is greater than 1:1.