What is SAN Fill Word?

This is snip from Brocade SAN Admin Best Practicies ...

Note: Fill Word (apply for 8 Gbps platform only)

Prior to the introduction of 8 Gb, IDLEs were used for link initialization, as well as fill words after link initialization. To help reduce electrical noise in copper-based equipment, the use of ARB (FF) instead of IDLEs was standardized. Because this aspect of the standard was published after some vendors had already begun development of 8 Gb interfaces, not all equipment can support ARB (FF). IDLEs are still used with 1, 2, and 4 Gb interfaces. To accommodate the new specifications and different vendor implementations, Brocade developed a user-selectable method to set the fill words to either IDLEs or ARB (FF). Currently, setting the fill word can be done only via the CLI command portCfgFillWord (Ex: portcfgfillword [slot/]port, mode). There are four modes:

Mode 0 - Use IDLEs in link initialization and IDLEs as fill word (default mode).
Mode 1 - Use ARB (FF) in link initialization and ARB (FF) as fill words.
Mode 2 - Use IDLEs in link initialization and ARB (FF) as fill words.
Mode 3 - Try Mode 1 first; if it fails, then try Mode 2.

Traffic outside of frame traffic is made up of fill words: IDLEs or ARB (F0) or ARB (FF). Encoding errors on fill words are generally not considered impactful. This is why you may see very high counts of enc_out (encoding outside of the frame) and not have customer traffic affected. If many fill words are lost at once, the link may lose synchronization. On standard E_Ports, primitives are set to ARB, regardless of the portcfgfillword setting when not in R_RDY mode.

The recommended best practices are:

• Ensure that the fill word is configured to Mode 3.
• When connecting to a HDS storage device, set to Mode 2.
• When upgrading firmware, recheck the settings, since the fill word primitive has evolved over several Brocade FOS releases.

Brocade Secure SAN Zoning Best Practices

White Paper
http://www.brocade.com/downloads/documents/white_papers/Zoning_Best_Practices_WP-00.pdf

This paper describes and clarifies Zoning, a security feature in Storage
Area Network (SAN) fabrics. By understanding the terminology and
implementing Zoning best practices, a Brocade®
 SAN fabric can be
easily secured and scaled while maintaining maximum uptime.
The following topics are discussed:
• Zoning defined and LUN security in the fabric
• Identifying hosts and storage members of a zone
• How do SAN switches enforce Zoning?
• Avoiding Zoning terminology confusion
• Approaches to Zoning, how to group hosts and storage in zones
• Brocade Zoning recommendations and summary


What is Zoning?
Zoning is a fabric-based service in Storage Area Networks that groups host and storage nodes
that need to communicate. Zoning creates a situation in which nodes can communicate with
each other only if they are members of the same zone. Nodes can be members of multiple
zones--—allowing for a great deal of flexibility when you implement a SAN using Zoning.
Zoning not only prevents a host from unauthorized access of storage assets, but it also stops
undesired host-to-host communication and fabric-wide Registered State Change Notification
(RSCN) disruptions. RSCNs are managed by the fabric Name Server and notify end devices of
events in the fabric, such as a storage node or a switch going offline. Brocade isolates these
notifications to only the zones that require the update, so nodes that are unaffected by the
fabric change do not receive the RSCN. This is important for non-disruptive fabric operations,
because RSCNs have the potential to disrupt storage traffic. When this disruption was more
common, that is, with older Host Bus Adapter (HBA) drivers, RSCNs gained an undeserved
negative reputation. However, since that time most HBA vendors have addressed the issues.
When nodes are zoned into small, granular groupings, the occurrences of disruptive RSCNs
are virtually eliminated. See a discussion of single HBA zoning in the section of this paper
entitled, “Approaches to Zoning.”