Is there any potentially problem if I adding a link between SAN A and SAN B?

[Hele Du]

Hi Experts,

I am confusing with SAN A and SAN B separation.

If i adding a link between SAN A SAN B, is there have any potentially problem? like the attachment.

From my opinion, the SAN A SAN B are merged together and only need configuring zoning once,  the traffic also in HA mode.

Please correct me if anything wrong , thank you so much.

[dynamoxxx]

You absolutely do not want to do that. There is a reason they are two distinct fabrics.

Take a look at this document and the documents linked at the bottom of the pdf

https://supportforums.cisco.com/document/12125891/large-san-design-best-practices-using-mds-director-class-switches.pdf

[Hele Du]

HI Dynamoxxx,

Thank you for your reply.

I had read that document before, it noticing below:

It is common practice in SAN environments to build two separate, redundant physical fabrics (fabric A and fabric B) to protect against the failure of a single physical fabric

I don`t know how does the one fabric design will cause single physical fabric failure.

If there some switch failures, the one fabric design also provide forwarding from server to storage or vice versa.

[dynamoxxx]

Logical failures more than physical switch failures (zoneset corruption, human errors)

[Hele Du]

HI Dynamoxxx,

Thank you for your reply.

Do you mean that one fabric design is more easy to make mistake with configuration.

If there are some wrong configuration in one fabric it will impact all fabric?

What will happen if the middle link break-down bewteen two MDS?

I think the zoneset configuration will be retained on each MDS ,right?

[Walter Dey]

I remember that IBM was always claiming, that achieving availability of 99.99 (or even 99.999) requires a physical dual FC fabric. And this same philosophy is shared by all major storage companies.

[Hele Du]

Hi Walter,

There is also a design called “Single Fabric, resilient” in brocade SAN design guide .

I think there must something drfference between these two design.

[dynamoxxx]

can you provide a link to the document where you saw that ?

[Hele Du]

Hi,

The link is below, the design is in section 2.

http://www.brocadechina.com/download/ssc/53-0000231-03.pdf

Although，they mention four design, but the “Dual fabric, resilient” is more recommended. Because it can reduce 50% routing table and the size of FCNS database.

Back to our topic, I think the dual identical fabric is more easy to extension and maintenance.

[dynamoxxx]

it talks about resiliency within a single fabric as far as switch failure or ISL failure, it will not save you from human error if someone accidentaly deletes zoneset.  You have come up to the right conclusion, use two separate fabrics.

[Hele Du]

Hi Dynamoxxx,

Thank you for your doing.

It is really my appreciate!