What's better with two switches: only one fabric or two?

[Carlos F. Baladrón]

I have two switches Brocade 4/64 with 10 HP-UX and Windows 2003 servers, a XP12000 (8 ports connected to each switch) and a tape library. Most of the servers are configured with two FC adapters, one in each switch.

What's the best option for the SAN:

A) Configure two independent fabrics, one in each switch.

B) Configure an ISL between the switches and set up only one fabric.

Are they the same or are there any pros or cons?

Thank you in advance.

[Mark Poeschl_2 · Accepted solution]

I would recommend two separate fabrics - that way if some component went berzerk in one fabric you'd still have a fabric capable of supporting operations.

The other downside of connecting the switches is that now each HBA will have twice as many paths to each disk - half of them will be "efficient" (i.e. one hop) and half of them will be "less efficient" (two hops). I don't think the driver in the server would have any way to distinguish between the two.

[V.Manoharan]

Hi carlos,
I prefered to go with two fabric since you design the redundancy in the san environment since you have got two FC adapters in each servers.

regards
Mano

[Steven Clementi]

Carlos:

HP recommends that you configure in a way to provide a "No Single Point of Failure". In following this rule... you have multiple paths to storage, multiple HBA's, multiple switches... You need to keep things separate in order to be sure that 1 item does not effect the 2nd like item.

In other words, you want 2 independent fabrics.

If you configure as only one fabric, changes you make can potentially effect ALL of your devices on the SAN. By having 2 separate fabrics, any change you make on fabric "A", will not effect Fabric "B".

Definitely not the same.


Steven

[Carlos F. Baladrón]

If, this undoubtedly with 2 fabrics the changes in one would not affect to the other one and also the fact of have Not â Singe Point of failureâ , but in the supposition that a switch (case b) Down could I continue working with the switch that this up without lost of service.

I ask this because for the client their main priority is to have the services up in the case of failure of a switch.

Not I understand what you mean with half of them will be "efficient"

[Uwe Zessin]

If you connect both switches, you have created one management domain. An error will affect the whole domain. Two separate switches will create two management domains.

The additional paths resulting from the ISL do not provide much added protection: e.g. the failure of a single end-node port is not compensated by the ISL.

[Carlos F. Baladrón]

You are right Uwe but, we don't want to get additional path we want to get it is high availability; in the case of failure in a switch

[Uwe Zessin]

Well, then don't connect them (option A) so that a human/software error on one switch does not affect the other.

[Steven Clementi]

If you have only one fabirc, the failure of a switch could potentially cause fabric wide problems. You want to have 2 separate fabrics for High Availability.


Steven

[Carlos F. Baladrón]

Thank you to all for the answers, this clearing the best option is 2 fabric (case a)