should I connect two libraries to one switch?

[zhaogui]

I have a SAN environment consist of two Broadcade switch,two Ultrim tape libraries,VA7400 and three HP-UX servers, but there is only one FC card on each tape library. Should I connect both tape libraries to one switch or one library to one switch? That is,
Lib1,Lib2 ==>SW1 or
Lib1=>SW1; Lib2=>SW2
Thanks,

[Duncan Edmonstone]

I guess it depends on:

a) Your switch topology... will you be using any ISLs?
b) The performance profiles for your systems
c) The availability requirements.

With no more information though, I would probably go for one library attached to each switch

HTH

Duncan

[zhaogui]

What's ISL? I am new to Broadcade switch.
Our SAN environment is purely for a 3-node cluster and there is no zone inside the switch. For all servers and VA we all use fabric.

Initially we only setup one library and used Fabric or "F-Port", recently after another library added on, then HP engineer just connected it to the same switch as for the first library and also changed the setting for the library from "F-Port" to "L-Port", I really don't know why. Can anybody shed some light?

[Duncan Edmonstone]

ISL is an inter-switch-link - I think it would show up as an E-port on brocade...

As for your library being attached via L-Port, this may be due to the type of bridge FC-SCSI bridge or controller you are using with the library - not all bridges/controllers support 'fabric logon mode' (F-ports) and have to operate in arbitrated loop mode (L-ports).

HTH

Duncan

[Michael Tully]

Hi,

As long as the switch communication is
the same, i.e. fabric and that you have
the zoning correct for each of your
ports. If you have an ISL, usually
associated as having a link in between
two switches, they would still have to
communicate with the same topology.
If you have these rules in place, I
do not see too many problems.

Cheers
~Michael~

[zhaogui]

There is no link in between Broadcade switch in our environment, But the VA7400 has two controllers and each server all got two HBA. I believe ISL occupy one slot on each switch as an overhead? Can you tell me what's the difference among these F-Port, E-Port,L-Port?

[Michael Tully]

Yes having an ISL slot on each switch is a
small overhead, but it can also be a used
as a failover point, like one library going
down, you could re-direct essential backup
transaction logging to the other tape library
without too many problems. Also where one
switch is not useable all traffic will resort
to going through the seond switch.

F-Port = Fabric
L-Port = Loop
E-Port = ??

What I would do in your situation is do this:

Server A HBA port 1 --> switch 1
Server A HBA port 2 --> switch 2

VA7400 SPA --> switch 1
VA7400 SPB --> switch 2

It is up to you whether you want to use and ISL.

[zhaogui]

Thank you for your quick response.
For VA7400-end and server-end connection, yes, we are using exactly the same kind of connection as you mentioned above. This is because all of them got at least two controllers and on server side we implement alternate link. But for tape library, there is only one controller.
Do you mean if I implement ISL between two switch, it can bypass the faulty one if one switch failed?
Or do you mean it makes no difference on how to connect my tape library since there is only one controller in the library?

[Michael Tully]

Having the ISL link between the two
switches is your failover point. The
idea is to reduce any failover points and
the ISL gives you this.

For example, on 2 x 8 port switches:

Switch one

Server A --> HBA 1
Server B --> HBA 1
Server C --> HBA 1
NT Server 1 --> HBA 1
Tape Library (1) --> SCSI/FC Bridge
spare
spare
ISL --> switch 2

Switch two

Server A --> HBA2
Server B --> HBA2
Server C --> HBA2
NT Server 2 --> HBA2
Tape Library (2) --> SCSI/FC Bridge
spare
spare
ISL --> switch 1

HTH
~Michael~

[zhaogui]

You still have not understood my concern.
Attached is the diagram for out SAN. Two libraries are connected to SW2. My concern is if I layed ISL, will I still be able to access libraries from my server when SW2 burnt down? Or do you think it is better to connect one Lib each to one switch?

[Michael Tully]

Hi,

The whole idea of having an ISL is so that
if switch number 1 dies, all traffic will
continue to go through switch number 2.
Switch 1 will have it's own configuration
and also a copy of switch 2. Switch 2 will
also have a copy of the configuration on
switch 1 as well as it's own configuration.

So, from your diagram, there will be no
problem if you have the tape libraries on
either switch or on the same switch. If the
ISL is configured and configured correctly
it won't matter which library is on what switch.

~Michael~

[zhaogui]

Thank you for your reply. But I was still wondering when SW2 burnt down how can this ISL link pass all traffic from two libraries, which were initially connected to SW2, all the way to SW1? In that case, it looks like two libraries can share the same port reserved for ISL at SW1?
And it also seems SW1 and SW2 forms a cluster and there should be a heartbeat sensor running at both SW1 and SW2 to detect the health status, so that one can take over another in case another fails.

But remember, if SW2 burnt down, no information can go through SW2->ISL->SW1 since SW2 is dead and it can't response/receive any message.
If each tape library got two links and one for each switch, then the answer is yes. I agree. But in my situation, there is only one controller for one tape library!