QuickLoop 126 "devices" limitation

[Scott Pelletier]

I'm reading the Brocade 2800 manual and it talks about a 126 "device" limitation. My question is what is a device? We're going to attach some HP/9000's to a couple Brocades and then to two EMC Symmetrix. We will have "a ton" of LUNs behind the FA ports on the Symm, but do these count as a device in this context? I'm thinking just the host HBAs and FA ports on the Symmetrix count as one each. If this is true, then you can consider each port on the switch maps to one device. What's a bit confusing, is that if only 2 switches are supported in a QuickLoop you would never come close to the 126 limit since the switches I'm reading about only have 16 ports each.

Thanks,
Scott

[David Lieberman_1]

Scott,

"devices" are nodes on the loop (HBA's, i.e. Fibre-Channel cards). Disks don't count.

(credit goes to our EMC Guru across the aisle.)
- David

[Bernd Reize]

You and David are right:
Each HBA, FA,.. counts as a device.

But there is a way to reach the 126 Device limit with only two switches: if you would cascade some host via hubs. but that's only theoretical, i would not recommend it.

[Oliver Haensel]

Hello Scott,

if a switch port connects with loop topology this loop will be isolated from loops connected to other ports in the SAN. Quickloop is a switch feature of Brocade to bring FC devices connected to different switch ports into one single loop.

In a loop every FC port gets its own Loop ID. That means every HBA, disk array controller, FC-to-SCSI bridge port, every native FC disk/tape drive will have its own and unique Loop ID in the loop. (Hub and switch ports (quickloop) are transparent.)

You can increase your fanout by connecting FC hubs to switch Quickloop ports. Also you can specify a so-called "quickloop partner" switch whose quickloop ports also join the same loop.
The number of devices and the cable length (especially for hubs) will affect the I/O performance of your loop. Every server reboot, FC HBA reset, cable disconnect or link failure will cause a loop reconfiguration which stops all I/O for that time (up to 2s). Therefore I would not recommend to have big loops.

Why do you need the Quickloop feature? If you'd like to use a FC HBA which is only capable to connect in private loop topology you would only see devices within the single loop(let) connected to the switch port you've chosen. Enabling the Quickloop feature allows you to access devices connected to other Quickloop ports.

But remember: HP limits the number of devices in a Quickloop for Brocade Silkworm2800 to 64! (legacy device support with HP9000)

-Oliver-