Brocade 8 Gbps Fibre Channel Switches and Fill Words
anthonyv 2000004B9K Comments (10) Visits (41640)
I thought I would write a quick post about an issue that's not new, but is certainly worth being aware of....
One of the interesting tricks with the change to 8 Gbps Fibre Channel is that it required a change to the way the switch handles its idle time... the quiet time when no one is speaking and nothing is said. In these periods of quiet contemplation, a fibre channel switch will send idles. When the speed of the link increased from 4 Gbps to 8 Gbps, the bit pattern used in these idles proved to not always be suitable, so a different fill pattern was adopted, known as an ARB. All of this came to intrude on our lives when it became apparent that some 8 Gbps storage devices were having trouble connecting to IBM branded 8 Gbps capable Brocade switches because of this change. This led to two things:
An example of what was said?
"Starting with FOS levels v6.2.0, v6.2.0a & v6.2.0b, Brocade introduced arbff-arbff as the new default fillword setting. This caused problems with any connected 8Gb SVC ports and these levels are unsupported for use with SVC or Storwize V7000.
In 6.2.0c Brocade reintroduced idle-idle as the default fillword and the also added the ability to change the fillword setting from the default of idle-idle to arbff-arbff using the portcfgfillword command. For levels between 6.2.0c and 6.3.1 the setting for SVC and Storwize V7000 should remain at default mode 0.
From FOS v6.3.1a onwards Brocade added two new fillword modes with mode 3 being the new preferred mode which works with all 8Gb devices. This is the recommended setting for SVC and Storwize V7000"
So there are several tips that I will point you to, depending on your product of interest:
Brocade Release Notes
For most environments, Brocade recommends using Mode 3, as it provides more flexibility and compatibility with a wide range of devices. In the event that the default setting or Mode 3 does not work with a particular device, contact your switch vendor for further assistance. IBM publishes all the release notes for Brocade Fabric OS here.