Hey all, Fibre channel at the drive level is a single 40 pin copper connector. However, unlike scsi, you don't often see single backplane devices to plug the drives into. That 40 pin connector supports two logical and physical "loops". So... Fibre devices (be it a jbod or an array or raid) often have two ports, an "A" port and a "B" port built into them. There is a 1GB standard and a 2GB standard (4GB and 10GB are already on the roadmap and/or in limited production for switches and cards and drives) You can have up to 126 devices on a fibre bus in "loop" mode (arbitrated loop) and then it acts like scsi but can be set up to "self configure" or you can use the chassis for drives to "SET" the loop id, aka the "ALPA" There is also a "fabric" mode where everything gets identified by it's "world wide name", which is the fibre channel equivalent of a MAC address. Then the basic limit is 16 million addresses. You can do fabric mode with arrays and raids and libraries, but not easily with regular jbod or disk drives connected to cards because in that limited environment. There are fibre channel hubs, and fibre channel switches, and both concepts are exactly the same as in ethernet, and for basically the same reasons. However, almost all switches in fibre channel are managed for zoning, etc... The interface, (copper or glass) makes no difference for fabric or loop mode (you will also here people say "point to point" mode which is fabric negotiation even in a "loop" topology, like when plugging a fibre channel raid directly into a server card. The 1GB fibre standard for copper was/is either a db9 connector with 4 pins uses, or an HSSDC connector, which looks more like a squished and wider ethernet port. The optical 1GB fibre standard looks the same as the original optical 1GB standard for ethernet, and is called an "SC" connector. The 2GB standard for optical is called LP, and is about 1/3rd the size, and uses the same style of connectors that the newest optical ethernet does, although the ports and cards and switches themselves are not usually interchangeable. There is a copper standard for 2GB but is rarely used and called HSSDC2. The last confusing thing is that some cards and switches and chassis use EMBEDDED ports and some use removable/replaceable ports. In 1GB, they call them "GBIC"s, and for 2GB they are called "SFP"s <shrug> So, the fibre standard allows for "daisy chaining" like SCSI does. As long as you have fewer than 126 devices on the loop. That doesn't mean you'll get good performance. <grin> Raids count as ONE device on a loop, if connected in loop mode. In general, if you are going to do LOOP things, you try to keep 16 or so devices on the bus. If you want lots of devices, use a hub. If you want/need more bandwidth, use a switch and/or use more fibre host adapters. <grin> Ted Letofsky <not a very good linux guy, but I know a little storage> -----Original Message----- From: tclug-list-bounces at mn-linux.org [mailto:tclug-list-bounces at mn-linux.org] On Behalf Of Nate Carlson Sent: Thursday, May 26, 2005 12:29 PM To: Florin Iucha Cc: tclug-list at mn-linux.org Subject: How does Fibre Channel work? [Was: Re: [tclug-list] Source forQLA2200's locally?] On Thu, 26 May 2005, Florin Iucha wrote: > If I want to connect three computers to an array, do I need a switch? > Does an array have a single port? (+ see below) Again, this is from my limited experience. All of the arrays I've worked with have two ports, which both connect you to the same loop. However, I know there are arrays with more ports, and arrays with only single ports. > I remember something about an "Arbitrated Loop" where the computers > and > storage sit in a circle and pass a pipe ;) Can I do that with copper, or > do I need something optical? Quick google search: http://www.seagate.com/support/kb/disc/fcp.html Doesn't explain it all that well, but as I understand it, the switch or hub is what allows your computer to connect to the loop of drives. Please, someone correct me if I'm wrong! :) ------------------------------------------------------------------------ | nate carlson | natecars at natecarlson.com | http://www.natecarlson.com | | depriving some poor village of its idiot since 1981 | ------------------------------------------------------------------------ _______________________________________________ TCLUG Mailing List - Minneapolis/St. Paul, Minnesota tclug-list at mn-linux.org http://mailman.mn-linux.org/mailman/listinfo/tclug-list