Gb ethernet question
 

I have a wireless router which has 4 10/100 jacks. I feed one of the jacks to an 8-port switch, and everything connects to the switch. Works well.

I'm looking at upgrading the internal network to 1 Gb. My initial plan was to install an 8-port 10/100/1000 switch and connect my desktops to the RAID server. All will, naturally, have 1 Gb NICs. For connecting to the internet, the 100 Mb link to the router will be more than adequate.

My thought was that if I connect desktop A to RAID server B, the transfer will go through at (something like) 1Gb. However, on further reflection, it might be that the signals have to go through the router, which cannot handle anything above 100 Mbs. So, I would have to upgrade the router as well.

Is this the case or am I missing something?

Since everything is on your LAN, there is no routing involved. If the RAID and your computer are both connected to the same switch, then nothing goes through the router because there is nothing being routed.

Note that 1 Gb/s is about 125 MB/s. This is the theoretical max - it's unlikely that a consumer grade switch will yield such a speed.

OK - but ...

If I, say, map the drive on my RAID to my desktop, I talk to it using, what? ... TCP/IP? The RAID has a static IP, but how does the switch know where to send the data? Does it "ask" and see who responds, and then set up a virtual connection or what? If it's something like that, then, sure, I don't need a router. What if it's a DHCP-assigned IP?

I confess, the actual detailed nuts-and-bolts of just what's going on down there is a little vague to me.
Oh, I know. And I'm undoubtedly not getting 12.5 MBS out of the current setup.

But a ~10X increase would be most welcome.

OK - I tried it out.

Disconnected the switch. I can't reach the internet at all, but I can ping and access everything else on the LAN..

So, I guess it'll work.





Still not sure exactly how it does it all, though :)

Congratulations! Like magic, isn't it? :D

Try not to obsess about why you're not getting theoretical performance.

Yes, your desktop is communicating via TCP/IP with the RAID server.

The switch doesn't know anything. It's just a pipe that connects your computer and RAID. Well, a smart switch would be able to do some processing of the data, but a standard dumb switch doesn't really, beyond inspecting each packet to see which MAC it's going to and directing the packet to the appropriate port on the switch. In contrast, a hub (which you don't really see anymore) would broadcast all packets to everything connected to it.

At the very low level, I think that your PC will send a broadcast over the local network to ask who has the IP address of the RAID server. The RAID server will reply with its MAC address, and then your PC connects directly using that.

A DHCP-assigned IP doesn't make a difference. Your router is presumably your DHCP server. When a network device requests an IP, the router assigns it one. The device hangs on to that IP until I think halfway until its lease expires, at which point it requests another one. If the router isn't available on the network at that point, eventually the IP lease will expire and the device will lose its IP.

I generally dislike "magic" - I'm never comfortable with stuff that "just works", 'cuz, if it goes south, I'm at a loss as to what to do. And I know why you never get the theoretical max out of a comm link.
OK - I now have a mental picture of what's going on (in a gross sense, at least). No magic. :)

So - long and short, I should be able to pump stuff back and forth to/from my RAID server (and/or the other desktops) without having to upgrade the router.

The wireless is G, so the laptops are limited to 54 MB/s max (which they'll never see) but they don't use the other computers much anyhow.

Perfect!

PS - This little discussion has saved me a lot of googling and time spent sussing out what the "gurus" are really saying. The problem is, they have to address a wide range of readers and the discussion isn't really interactive. Ol' Dave, though, is usually hanging around and jumps in with answers to specific questions. Gotta love it. ^

Under everything new, the last Ethernet hop is still resolved via ARP (Address Resolution Protocol)... which is a form of broadcast. When the n-1st switch realizes the nth and final hop is on the same network, it does exactly what you thought asks "who has", and then the packet travels to it's destination...

Consumer grades switches handle it just fine, especially if you're only talking 1-2 streams at that speed (even so, most of them not have enough backplane bandwidth to do a half-duplex connection at that speed on every port; full duplex, somewhat less frequently.)

The NICs and the OS are far more likely to be a problem. Decent NICs and Windows file sharing seem to top out at about 110MB/sec, which if you think about protocol and signalling overhead and latency is pretty darn good.

Some protocol running on top of TCP or UDP, most likely (both of which run on top of IP). If Windows, probally CIFS (or its older version, SMB.)

It sits and waits for something else to connect.

Doesn't matter how the IP is assigned. Once two machines have IPs on the same subnet, they use a protocol called ARP to find one another. That involves a few broadcasts, basically "Hey, is 192.168.0.2 out there?" "Yup, I'm here, my MAC is 12:34:56:78:90:12" after which the first machine knows to send directly to that MAC address for that IP address.

If you're using Windows file sharing, the way it works if your PC sends a TCP connection request to the RAID asking to open a file sharing connection. The RAID only knows that someone at that address is connection, and their credentials (if security is set up.)


Blow $4 on Amazon and buy this book used (or get it from the library, or do the same for some other basic networking text):
http://www.amazon.com/Internetworkin.../dp/0130183806
...a bit dated, but well-written and hey, a penny + $3.99 shipping for a classic, how can you lose?

802.11G is 54Mb(its)/sec, not 54MB(ytes). With decent cards and good software -- and a good signal -- you should see file transfers around the hypothetical limit of a little less than 6.75MBytes/sec.

--

BTW, since ISTR you have said you are still using XP, you may want to look up tunings for the network stack to speed up file transfer... my recollection is that back in the day there were some registry tunings (TCP window size maybe?) that sped up transfers on XP a lot when I went to gigabit (on Vista/7 and most modern Linuxes, they're self-tuning these days.)

Sorry if I came across as flippant. I've had a home network since the days when Windows did not have its own networking stack and learned a lot in the intervening years.

As nkedel points out, for the level of knowledge you aspire to, read a book on the subject. Modern networking is quite fascinating and can even make you obsessive about tuning it :D