How does SAN prevent loops?

[Cooky]

I'm new to storage area networks.
I've done very basic stuff like a few VSAN's on a 9100 MDS, but nothing complex or fancy.
Is there something similar to the spanning-tree in the ethernet world, that prevents loops?

If I have two links between two MDS boxes, will both links forward traffic, or only one?

 

[imagoon]

SAN's are not special compared to an enterprise network. You make sure you don't have any loops. Since the SAN rarely leaves the dataroom, you have no need to worry about users looping ports out in the office or anything. Each port on the SAN device is just a host (not a switch) just like a computer or server. When you configure the initiators you tell it that a LUN is available at a "device" and point the initiator at all or a subsection of the ports.

I guess I should elaborate a bit.

There is several ways to do something like Fiber channel. 2 dedicated links to each device or rings (where a loop would be done on purpose.) There is a protocol running inside the FC that can do loop detection and break a connection like STP. You do this for redundancy in a broken link situation. FC is lot like a normal physical ethernet network in physical layout on paper. The medium and the protocols are different and more geared towards storage system needs more than workstation networking.

 

[her209]

FC or iSCSI?

 

[Cooky]

Thanks for the quick responses.

This is for FC.
I'm asking because we're adding more MDS SAN switches, and need to create an "ether-channel" between the existing and new MDS box to support higher bandwidth.
Was just wondering:
1. does MDS support the ethernet equivalent of ether-channel?
2. what if we simply use two links for redundancy purpose, but don't do ether-channel, how do the MDS switches detect and break loop (hence my original question)?

 

[spidey07]

I don't know specifically but FC has built in bonding and a control protocol regarding loop prevention. I can't for the life of me remember what they're called and I'm not at work to ask our SAN gurus.