1.2 Flow Vision

This subject will be divided in two sections.

  1. Flow Monitor and Generator
  2. Flow Mirror

In FOS 7 the concept of frame-monitoring was introduced on Condor2 and Condor3 ASICs. This allowed an administrator to create a frame template based on the FC frameheader (see here) and obtain statistics on these frames. Flow Vision is somewhat progressing on this technology and has been extended significantly. Flow Vision is a 3 way solution which requires a switch capable of providing the functionality, software licensed to be able to configure and capture flows and a tool to collect and interpret these flows. All Condor 3 based switches (16G), FOS 7.4 and up, and Brocade Network Advisor 12.4.x are needed to be able to fully utilise the base flow-vision functionality. (The Brocade AMP platform is an extension but will be discussed later.)

!!!! Important !!!!!

A fibre-channel switch, whether from Cisco or Brocade, is not an FC analyser. Although both have extensive capabilities when it comes to monitoring and giving insight into traffic patterns it does not provide the same level of insight an Ancor or JDSU Xgig can. Do not make the mistake of using a switch as an IO performance monitor.

Although all three options use the same underlying technique they do have different purposes. Flow Monitor provides a statistical overview of traffic patterns allowing you to adjust your fabric design and initiator to target mapping. This insight will result in a better picture of your environment and allows a more balanced fabric with less hotspots and overall higher performance.

Flow Generator will be most often used in a green-field installation or when new links are getting utilised especially in a campus or metro environment. Flow Generator allows you to send a fairly extensive set of traffic patterns between a configurable source and destination port. In addition to D-port functionality Flow Generator gives a better insight into overall fabric and link capabilities. D-port functionality is more dedicated to a single link and is able to characterise the physical aspects before it is been put in use.

Flow Mirror is best viewed as a SPAN port option which allows you to capture frames. These frames can be sent to an externally attached analyzer or to the local embedded processor. The latter has a limitation of only 250-frames per second so is not suitable for capturing traffic in high performance set-ups but is very valuable in diagnosing connectivity problem where a host can’t see a lun or fails to log into a fabric for whatever reason.

Flow Monitor

As with all monitoring software it is imperative to “know what you want to know”. Simply turning it on and do garbage collecting will never work. It never has and never will be. Do the analytics on your requirements first and configure Flow Monitor as such. It is not prohibited to use wildcards in the FM configuration but to use a “catch-all”/”collect all” kind of approach will drown you in data and will not provide you with the information you want.

As soon as you know what you want create specific monitors and apply them sparsely. Take a step-by-step analytics approach to hone in on issues you observe or to get indications how to design traffic flows. There are a fair few options and limitations but please consult the manual with each FOS-code level in this case as this is an area of fast moving development especially in conjunction with the AMP equipment.

Flow Generator

Flow generator is very helpful in creating traffic patterns over specific ports in order to be able to establish a base-line on performance, link characteristics and cross-traffic impact analysis. Especially having the ability to create different traffic patterns allows you, or support personnel, to check if certain bit-patterns can have a negative impact. This is most helpful when checking ISL’s and long-distance connections over CWDM/DWDM and FCIP.

Be aware that FG is a non-limited generator which basically means it generates traffic at line-speed and will thus fill up a link very quickly. This can, and most likely will, have a significant impact if production traffic is using the same links.

Flow generator used the concept of so called simulator ports. This is a Brocade proprietary port status where the PSM (Port State Machine) is creating a virtual attached device including FCID’s and virtual WWPN’s. These can then be used to create traffic from A to B, B to A or bi-directional.

As of FOS 7.3.0 there is a special flow called sys_gen_all_simports. This flow is specifically handy if you bought a brand new 16G or 32G  switch and want to test all back-end connections in order to be able to check if there are no back-end link issues. I would seriously advise to do this test as it may prevent numerous troubleshooting sessions to try and see why some hosts or arrays have connectivity issues. Again check the manual for the appropriate syntax.

Flow mirror is in the next post.

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