[K12OSN] Re: Large scale implementation in the pipe

[John Baillie]

Well done Jeff maybe this should go in the Wiki.


> 
> Message: 2
> Date: Thu, 19 Aug 2004 20:28:59 -0400
> From: Jeff Kinz <jkinz at kinz.org>
> Subject: Re: [K12OSN] Large scale implementation in the pipe, input
> 	needed.
> To: "Support list for opensource software in schools."
> 	<k12osn at redhat.com>
> Message-ID: <20040819202859.A5196 at redline.comcast.net>
> Content-Type: text/plain; charset=us-ascii
> 
> On Fri, Aug 20, 2004 at 12:23:45AM +0200, Daniel Hedblom wrote:
> > Hello Norbert!
> > 
> > So, a server handling about 150 clients would be how big? Ofcourse those
> > wouldnt all be running at the same time at full load. The reason i ask is
> > that i would want to be able to do an estimate on just how big of a server
> > it would have to be. I want to have solid ground  under my feet and not
> > just my own experience.
> 
> Hi Dan. 
> 
> How much do you have the students environment locked down?
> 
> I have a one installation where we have the the Thin clients(TC)
> absolutely locked down so they can only run OpenOffice and a browser.
> For each TC we try to add about 100MB to the server. 
> 
> We want to make sure that swap is not used by the TC's since having to
> swap memory over an NFS link is really slow and eats network bandwidth.
> 
> So 150 TC = 100MB * 150 = 15000 MB or 15 GB.  Caveat - the more TC's
> you add to the server, the smaller memory increment they require.
> 
> This is due to the net gain of shared libraries already resident when
> many TC's are running the same apps.  So, ultimately this very 
> straightforward, linear estimation may cause you to get more memory than
> you need.  Of course if you know in advance how many TC's will be
> running what apps at the same time you can get a much better estimate of
> your memory requirements.  
> 
> Now go look up how much more memory costs per GB when you have to buy
> multi GB sticks.  (Pricewatch says 1GB stick is $150 to $247, but they
> are always low)  2 - 1Gb sticks from HP for the "Proliant" system is
> $1149  But .. its warranted for life.. (Funny, so is the stuff from
> Crucial.com thats faster and a tenth of the cost... how strange... )
> 
> A 4 Gb stick is $1700.00 -- I see a trend... 
> 
> If your TC's are not locked down and the students have access to the
> entire set of menus on the desktop then you may need more than 100 MB
> per TC. (you can process limit them so they can't open umpteen apps
> at the same time)
> 
> 
> As for CPU requirements, A 2 GHz , low end CPU can run 10 TC's which 
> aren't too busy.  For your system with 1 server, you want a machine
> with as many SMP CPU on it as you can find. at least four and eight is
> better, and you want high end CPU's.  XEON's or whatever the current hot
> chip is.  Again, you'll pay a premium over the commodity level
> components.  3 to six times as much. (Low end CPU is $60) High end is ?
> 
> In addition to being much more expensive, the centralized server
> architecture is riskier and more problematic than having a server at
> each location.
> 
> Its weaknesses are:
> 
> 	Single point of failure.  If the server goes down, service
> 	does not degrade "gracefully", it disintegrates. 
> 
> 	With multiple servers at least many thin clients(TC)
> 	would still be able to function,
> 
> 	Increased dependence on unneeded network links.  With the 
> 	server in a remote location from the TC's it is serving rather
> 	than at the same location as the TC's it is serving, the risk of 
> 	a service failure is increased because it is now additionally
> 	dependent not only on the server running but also on the network 
> 	links being intact (think backhoes, manhole fires,
> 	automobile/telephone pole accidents etc..) and dependent on the 
> 	network equipment, (Router, switches etc)  running as well. A
> 	final vulnerability is the vendor/supplier who is running those
> 	comm lines for you.  If they have any issues (strikes, software
> 	glitches, security compromised), your connections between
> 	buildings are affected and you lose service.
> 
> 	Another network issue is the plugged pipe problem.  This much
> 	X-Windowing will generate a huge amount of traffic.  OK maybe 
> 	1 GB net with smart switches can handle it.  But what happens
> 	when you add streaming video being accessed by 40 or 50 TC
> 	simultaneously?  Many legitimate curricula present their 
> 	content this way, but as these types of content multiply and
> 	become more diverse, can your network handle the additional
> 	traffic?  Better to use a design that inherently reduces the 
> 	network load from the get go.
> 
> 	Increased dependence on software integrity.  In the centralized
> 	scenario, if any single process consumes more than its share
> 	of machine resources everyone sharing the single server is hit.
> 	(Setting disk quotas, memory and process limits will help
> 	prevent this)
> 
> 	Security issues - One successful attack means all your resources
> 	get owned and leaves you with no untainted system to use as a
> 	base to work from.
> 
> 	Expense?  The initial outlay for the single high end machine
> 	that would be required to configure a server of the size needed 
> 	would have a premium of added cost high above the cost
> 	of the same power/capability obtained by purchasing multiple
> 	smaller off-shelf machines.
> 	
> 	Scaling issues?  multiple versus 1 central server(s), each has
> 	their own set of issues.