Re: [Xen-users] Server purchase pointers

["Luke S. Crawford" <lsc@xxxxxxxxx>]

On Fri, Feb 24, 2012 at 03:11:00PM -0500, Javier Guerra Giraldez wrote:
> On Fri, Feb 24, 2012 at 5:05 AM, Bart Coninckx <bart.coninckx@xxxxxxxxxx> 
> wrote:
> > I've been assured that the line performs close to a LAN connection.
> 
> 
> don't believe that until you see hard round-trip-time numbers.  LAN
> latencies are under a single milisecond (unless badly configured), but
> even short WANs are hard pressed to go under 10msec.
> 
> WAN vendors like to say "it's like local LAN", but they omit that
> they're talking about bandwidth, not latency.  and for other
> latency-sensitive protocols (SMB file sharing is one of the worst),
> they have specific 'accelerators' (in short, big proxies cacheing most
> of the metadata going each way).  if you deploy your own 'weird'
> protocol, you're on your own, and get the whole ugly scene.
> 
> 
> but, if you ge your own dark fiber, then it might be just right!  (if
> you do good traffic shaping.... a whole dark art on its own)

Why would you need to do traffic shaping on dark fiber?  with simple
10G-LR optics you can do 10G over a pair.  I'm currently 
experimenting and haven't gotten a working system up yet, but 
I /think/ for under ten grand in used dwdm stuff, I can do 30x that.   
With real money, you can get a giant wad of 100G channels;  you can do
multiple terribits/sec with modern DWDM gear and 100G optics, but again,
we're talking real money.  

As far as I can tell, once you pay for the fiber, you can incrementally
add bandwidth, 10G, 40G, or 100G a wave.  

I'm experimenting with this now;  There is cheap municipal fiber in 
santa clara, and I have a friend with a bunch of surplus cisco
15540 units;  Sure, they eat half a rack, but they are cheap and
you can get a whole lot of 10G waves over a single pair with them.
Active, too, so your 'client' interface is just a whole bunch of
10G-LR optics. 

The problem with dark fiber (I mean, the problem besides finding
what links are in the ground.  Even the municipal fiber places only
publish very rough maps before NDA)  is going to be the distance.  
I mean, as another poster pointed out, you can't go faster than light.
But, if you are going within a city and your gear is good, you might
be close to the 'lan performance' you are talking about.

Now, if you buy a lit wavelength on fiber lit by someone else, 
again, unless they are oversubscribing (and as I said, there's no
reason to oversubscribe a dark fiber run, unless it's a really 
long dark fiber run, and a 'wave' or 'lambda' usually refers to
a dwdm channel, meaning it can't be oversubscribed)
performance should be the same as having your own dark fiber
run.

Of course, when buying 'lit' point to point links, I find that it's
often hard to get the sales people to distinguish between a 'wave'
(a non-oversubscribable link)  and a mpls connection (an oversubscribable
link)  and everyone oversubscribes when they can, and nobody admits
to it, and further, the cost of a 10G lit connection, in my 
experience, is pretty close to the cost of a pair of dark fiber
(note, I only explored this over short runs, namely from 55 s. market
to 250 stockton in san jose, and from place to place in santa clara.  
YMMV, etc, etc,  I'm a poor negotiator and it's quite possible that 
the economics are very different on longer runs, and I haven't actually
gotten anything working or signed any papers yet, so I could be 
completely wrong about all of this.)  


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