Brocade switch "roles"

[mack-xwWos]

Hi all, I just recently extended our switch fabrics by adding a couple of Brocade DS4100B 32 port switches to our 2 Brocade ED12000B's. Prior to the addition of the DS4100's my original switch was the principal. With the new 4100's added in they are showing as principal. Is it because the DS4100's are newer faster or higher code? Is there any issue with this? I don't see anything out of the ordinary but you know how that can sometimes come back and bite you....thanks....mack

[sysmgr1]

The assignment of the "principal" and "subordinate" switches seems to be arbitrary. I have about a dozen or so switches in each of my fabrics and it doesn't matter which one is the primary. It will float around. The important factor is to make sure that the switch configs of the new switch are compatable with the rest of them. The fabrics won't merge if there is a mismatch.

[GlenH1]

Hi Mack,

The principal switch election process is quite straight forward:

Any time a new switch joins the fabric, a principal switch election will occur.

The principal switch is elected based on 2 things.

1. The switch priority (ie: a switch definitely does wish to be principal). If only one switch wants to be principal, then it wins the election.

2. The WWN of the switch. If multiple switches have equal priority, then the switch with the lowest switch WWN will become the principal.

It is highly recommended with a large fabric in a core-edge topology that you make the core switch the principal as the principal switch must communicate with all other switches in the fabric for routing and fabric events. Selecting an edge switch as principal will place un-necessary Class F traffic on the ISL's connecting to the core.

For small/mesh fabrics, it is less important who holds the principal switch role.

It's also a good practice to make zoning and configuration changes from the core/principal switch.

For brocade, you can use the "fabricprincipal" command to set the switch priority.

There is some additional information on fabric design and principal switch elections in the EMC Networked Storage Topology Guide which is available from Powerlink.

Just one further note - the principal switch election process has nothing to do with the domain ID of the switch (for some reason many people seem to think these are linked)

Good Luck,
Glen

[mack-xwWos]

Thanks Glen, that's what I figured as well....just wanted to be sure...with only 2 fabrics I doubt it will make much of a difference but I am thinking of making the ED12000's principals. Response much appreciated guys...thanks.....mack

[sysmgr1]

The five year old article that GlenH refers to makes little sense concerning the switch roles. It makes no basis to the fact that it has any real affect on performance. The current Brocade publications on SAN design make NO reference to the principal/subordinate roles as being relevant or affecting performance..

It makes no difference if you do zoning changes from the primary switch or any other switches. It makes no difference as to what switch is principal or subordinate.

[GlenH1]

Hi Sysmgr,

You must have found an old link as that guide is updated regularly (Most recently July 2006) - try here:

https://elabnavigator.emc.com/emcpubs/esn-topo/wwhelp/wwhimpl/java/html/wwhelp.htm

It has a number of references on principal switch placement, but this probably sums them up best:

" One switch in the fabric is responsible for the distribution of domain IDs, and plays a role in the route creation for fabric management traffic. This switch is known as the principal switch. Since this switch must communicate with all other switches and is the basis for fabric traffic routing, this switch should be centrally located. This will assist in the uniform delivery of information in the fabric, and provide a consistent response to fabric build events. "

The document does have a slight error however where it says the following:

" Connectrix M-series switches have the ability to set a switch priority. EMC recommends that you set selected M-series switches to Always based on their location in the fabric. Connectrix B-series switches do not provide a mechanism to set the switch priority. EMC recommends that the B-series switches with the lowest WWNs always be located at the center of the fabric. "

Which of course is out-of-date as the fabricprincipal command can now be used for the B-series switches... I've sent a note for the doc to be updated.

Brocade make similar recommendations and also recommend that the core switch be the designated mangement switch in their brocade SAN designer certification study guide here:
https://www.brocade.com/education_services/pdf/BCSDNutshell-Apr05.pdf

Glen.

[JasonBailey]

The five year old article that GlenH refers to makes
little sense concerning the switch roles. It makes no
basis to the fact that it has any real affect on
performance. The current Brocade publications on SAN
design make NO reference to the principal/subordinate
roles as being relevant or affecting performance..

Brocade SilkWorm. Design, Deployment, and. Management Guide. SAN DDM. Version 3.0
http://www.brocadejapan.com/resources/tl/pdf/DDM_v3_0_53-0000366-03_C.pdf
page 127:
For Core/Edge topologies, the principal switch should be a core switch for optimal fabric operation. If using a SilkWorm 12000 or 24000 in the core, utilize it as the principal, as it has the greatest availability.

It makes no difference if you do zoning changes from
the primary switch or any other switches. It makes no
difference as to what switch is principal or
subordinate.

page 92:
It is important that the SAN administration team select one switch in the fabric as the administration switch. Using one switch for access lessens the possibility of multiple administrators making changes to different switches in the fabric at the same time.
Keeping in line with the terminology used by Secure Fabric OS, this switch is termed the primary management switch.
There are several reasons to select the core switch as the primary management switch for zoning, time services, Fabric Manager, Web Tools, and general administrative access.
The core switch is optimally located to communicate with all other switches in the fabric. The core switch is commonly the larger switch with a more powerful control processor. When zoning information is propagated, the switch where the zone
information changed is responsible for distributing the zone information to all other switches in the fabric. The core switch is directly connected to all other switches in the fabric.

[sysmgr1]

I'm sorry but the information you presented really doesn't make a valid case that assigning a principal/subordinate switch actually makes any kind of a difference.

Bottom line, if it makes you happy, go ahead and set it.