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SAN vs. NAS: What's that all about?

SearchNetworking's Dr. Network forum moderator Greg Ferro challenges the theory among storage area network (SAN) folks that Fibre Channel SAN is better than network attached storage (NAS).

So the other day I was doing some research on network attached storage (NAS). Then I had a look at storage area networks (SANs). Then I said to myself, "What is SAN vs. NAS all about?"

Now, don't get me wrong, we need to do something about improving hard disk drives (and storage in general). It's far better to have a whole pile of 'em stacked up in a single box, with a smart piece of electronics doing clever stuff. It's cool that you can dynamically reassign volume space, don't have worry about losing a drive because it's redundant, and swap them on the fly (hey -- no late nights!).

But how pointless is Fibre Channel, eh? Let think it about for a second. Fibre Channel is a highly specialized communications medium used to connect network storage devices together. Fair enough. Consider network-attached storage, where an open standard Gigabit Ethernet is used to connect storage network devices together. Hmmmmm, you spot the difference.

Dr Network: I'm sorry, did you say that your SAN is basically a whole pile of hard disk drives connected to a Fibre Channel switch?

SAN Bloke: Yep.

Dr Network: And you have these Fibre Channel adapters for file servers?

SAN Bloke: Yep

Dr Network: Why wouldn't you just use Gigabit Ethernet in full duplex mode? Lots of those adapters around.

SAN Bloke: Because Gigabit Ethernet isn't reliable enough.

Dr Network: Well, excuse me, I'll just go and tell that to the people using Gig Ether in their backbones today.

SAN Bloke: You don't understand, we have special requirements for storage

Dr Network: Pttthhhh, special requirements my butt!!!

I'm just old enough to remember things like Token Ring and FDDI. And I'm here to tell you that they were great technologies. I mean, really great. If you had a LAN using FDDI and Token Ring, you never had to work late, because you could disconnect and reconnect without interrupting your backbone. (I often measure a good technology by how often I have to work late to maintain it. Let's face it, you don't get paid any more at 2 a.m.)

But the market decided that Ethernet was cheap and therefore must be better. Eventually, us network geeks gave in and made the best of it. As an aside, that's why we have all those crappy add-ons for Ethernet today, like 802.1Q (stolen from 802.10 used in FDDI), VRRP, and multilink trunking (because you couldn't load balance Ethernet but Token Ring was designed to do that from the start)... but I digress.

So why have the SAN people decided that a whole new standard would be a good idea? I mean, we can make a Gigabit Ethernet switch that will do exactly the same thing. Hell, the Gigabit Ethernet physical layer uses the Fibre Channel physical layer anyway; the Gigabit Forum completely ripped it off!

Let's think about it. I need to make sure that my data gets where it's going in good time. Okay, I build a really fast non-blocking Gigabit Ethernet switch and make sure that the devices that connect to it don't overload it. And, voila, smells like Fibre Channel to me. (By the way, have you seen the price of a Fibre Channel switch? They're talking about ten thousand dollars a port.) I reckon that Fibre Channel is either a monopoly, or it's just a defense against bad implementation (after all, you ain't gonna overload your Fibre Channel switch when playing network Quake).

So I looked around a little bit more, and found iSCSI. Well, hello. I put my SCSI packets into IP and send them over the network. I can see a few problems here; someone who doesn't understand technology is probably going to connect his hard disk drives to a hub and then wonder why it doesn't work. But these days, most of us read the manual first. Sometimes we even pay attention.

If you are thinking about putting in a SAN, give it up. Look at network attached storage, and think really hard about what you are doing. Take the time to understand how it works. Design it carefully, don't cut corners, and it will work really well.

Mark my words, Fibre Channel looks just like Token Ring from where I stand, and who is implementing Token Ring networks today?


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