Dual Core or Quad Core?

[Warren Luebkeman]

On Friday 29 June 2007 10:08 am, Tom Buskey wrote:
> On 6/29/07, Warren Luebkeman <warren at resara.com> wrote:
> > I asked for a quote on a server yesterday from our hardware provider, and
> > the
> > sales guy told me about a great new deal.  For the same price as a Dual
> > Core,
> > 2 Ghz Xeon processor, I can get a Quad Core 1.6ghz Xeon processor.  My
> > first
> > impression was four must be better than two, but is it really?
> >
> > The server is supposed to be a 50 user Linux terminal server.  Our
> > current specs for this system are:
> >
> > Dual Processor Dual Core (4 Processors)
> > 6 GB Ram
> > 15K SAS Hard Drives
> >
> > So now I can build the same system, but with 8 processors vs. 4, for the
> > same
> > price.  My thought is because its a terminal server, the speed of the
> > processors is less critical to the number of processors you have, because
> > you
> > need to distribute the load of 50 users across one server.  I can't
> > imagine a
> > word processor running at 1.6 Ghz vs. 2 Ghz should perform any
> > differently.
> > So by moving to more processors, I should have less processes running on
> > each
> > processor, which according to my very rudimentary logic suggests that the
> > performance should be better, or at least, more efficient.
> >
> > What do you think?  Aside from the cool factor of having 8 processors, I
> > would
> > like to make the RIGHT decision regarding what server I buy.
>
> A few points:
>
> The Macintosh community had debates in the past about SMP vs single.
> Generally they think a dual 500 MHz is roughly like a single 700MHz.  From
> that subjective information, I'd say more cores that are slightly slower
> are better.
>
> I've felt that dual CPUs have lower latency when multitasking.  The OS runs
> on one CPU, software raid (why spend more for a dedicated hardware raid
> card?), your App on another, etc.  IMHO latency is more important then
> throughput for interactive use.

We use Adaptec RAID Cards for Driver/Support purposes.  Because its a terminal 
server will only configure RAID 1, because all we want to do is ensure that 
the server keeps running.  Data is stored on a dedicated file server.

>
> I've been looking at a VMware ESX server.  it's licensed per 2 CPUs.  A 4
> core is the same as a single or dual core in their licensing.  I'm finding
> with that, a dual quad core is cheaper then adding ram + 1 cpu to 2 systems
> with 3 single core cpus between them.
>
> Those 1.6GHz CPUs might use less power & generate less heat.
>
> The real limit on your application will likely be I/O.  Bus speed (FSB),
> network, disk speed, memory speed, etc.  How much data are they moving
> around?  More RAM will help more then CPU GHz also.

The servers are going into schools, so typically what happens is, a class 
comes in, logs into the system (all at the same time), and they launch 
Firefox or OpenOffice (at the same time).  There isn't really much data 
moving around.  Documents are stored on a file server, and we map the 
students drives when the login.  

So the biggest load on the servers is launching 30 OpenOffice or Firefox 
processes at the same time, which is why it would seem having more processes 
available would make sense.  We have noticed from our own experience that 
disk speed and RAM is more important, which is why we use 15K SAS drives, and 
put more RAM in the servers than is needed.  

-- 
Warren Luebkeman
Founder, COO
Resara LLC
1.888.357.9195
www.resara.com