[SunRescue] Fiber Channel, was RE: HBA's

[Christopher Byrne]

Behalf Of Al Potter
Sent: Monday, December 04, 2000 08:45
>HitechCafe has had cheapass FC drives for a while....
>
>	http://www.hitechcafe.com/eshop/product.asp?dept%5Fid=7&sku=ST19171FC
>
>Other similar good deals are out there....
>
>What sort of gear (controller, cabling, etc) is required to get this up and
>running, and is there an inexpensive controller option for Sparc (SBus,
PCI)
>or the PC (PCI)?


Ayup, like I said Fiber Channel drives are cehap, it's the HBA's and cables
that really kill you.

Okay the minimum for a Fiber Channel setup (or fibre channel if you're from
outside the U.S.) is an FC-AL HBA (Fiber Cahnnel Arbitrated Loop Host Bus
Adapter). This is essentially a combination of an extremely fast SCSI
adapter, an ethernet card, and a fiber optic bridge, since you can run
several different encapsulation layers over fiber channel. Remember FC is
just the physcal medium, and can be used for many different protocols. FC
devices are still SCSI, they are just using a serial fiber optic connection
(2 fibers usually) instead of 68 tiny copper wires.

In order to have internal drives you need to have an HBA with internal
ports, or a bridge from the inside of the case to your external ports, which
I don't recommend. Unfortunately most HBA's only have external ports.

You then need to decide on a connection standard. There are four or five
different connectors, but the most common would be SC. You also need to
decide on single mode or multi mode fiber (this effects your cabling,
switching, range, etc...). If you are smart you will get an HBA that allows
you to change modes and connectors through something called a GBIC, which is
basically a plug in module containing two small lasers, two small laser
receptors, and the connectors you have chosen.

Once that is done you need to get cables compatible with your choices. Once
again with internal drives this may be difficlut since most cabling, and
most HBA's in fact are made to go from HBA to HBA(loop mode) or HBA to
switch (fabric mode). While it is tehnically possible to make your own
cables, I recommed against it. Unless your cable run is very short you need
to highly polish the ends of the fiber before terminating it with
connectors, otherwise you get a large amount of refraction, and your data
can be lost. And premade polished fiber is not cheap, though to be honest
neither is high quality SCSI cabling.

In order to connect to multiple devices you need to have either a switch, a
hub, an MDF (media distribution facility), or you could just have a
controler with multiple ports and add another fiber. I'm not sure what Sun's
deal is on their new workstations, but judging from how they handled their
SCSI cabling in the past they probably just put in a very simple MDF with
connections to each drive bay.

Overall fiber channel is actually no more complicated than copper paralell
SCSI is, but we are much more familiar with copper, and used to it's
complications. Fiber is a relativley new world to most of us, and it just
sounds a lot more difficult. But believe me, being able to connect every
machine in your building to a single storage array with a couple of hundred
devices all on the same fabric, and never have to worry about cable length
is a joyful thing.


Chris Byrne
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