Best way(s) to speed up lab?

[Gavin McCullagh]

Hi,

On Sun, 30 Aug 2009, Harry Sweet wrote:

> Is there any specific switch you recommend?

We're somewhat caught between a tight budget and a need for good functional
switches.  Over time, we've found the D-Link DES-3550 and DES-3526 are
affordable, stable and functional.  They do multicast properly, we can add
layer 2 filters (eg we can block rogue dhcp servers).  In my experience,
the DGS-12XX (the G means fully gigabit) have problems with multicast, 
don't do filtering and have no serial port.  Those among others issues have
led us to write them off.

I can't comment on the other brands as I don't know them well.  Needless to
say, Cisco are the industry favourite, but come at a cost.  If I were
buying from another vendor, I would still require the same features, such
as layer-2 filtering, serial port (not just a web interface), gigabit
uplinks, snmp, vlans, spanning tree with edge/portfast, radius.

Apologies if some of these features are not familiar ground for you.  Our
choice of these features is based on the fact that we actively use them.
If you don't need them, that's fair enough.  It's most important to make
sure you have a gigabit backbone, ie that the links between all switches
are GigE.  If you have a 100Mb/sec line in there, everything will be
constricted by it.

> School starts next week, so for now I just have to work from memory.

Fair enough.

> We started last year with 2 gigs ram only.  Lagging would consistently
> start after ~16 machines logged in.  I could see us hitting virtual memory at
> the same time.  more memory solved that.

You have 8GB of ram now.  Is this a 64-bit linux or are you using a large
memory kernel?  Just make sure your kernel is able to use the full 8GB.

> Not all workstations would lag, either. But all apps on lagging boxes slow way down.  
> The machines don't lock up, just get very droopy.
>  I'll watch that this fall.

I wonder what the lagging ones have in common.  Are all the clients on the
same switch?  Is it possible the lagging ones are on one switch and the
free ones are on another?  I imagine when you had the previous RAM-related
issues that would have affected every client?  

> But Firefox seemed to always be an issue.  Especially since kids like to use it
> to waste time playing on line video games, or watching videos.  

Do you have flash installed?  Is it a requirement?  It seems to be a big
problem quite often (and it could be removed if you wanted).  The
flashblock plugin can reduce the amount of spurious flash adverts that get
loaded.

> I should be able to make that a lot less interesting this year if I can
> get my firewall/whitelist working.

One possibility you might look into is to make the browsers use a squid web
proxy for web access.  Squid allows you to make all manner of decisions
about what is and is not allowed and for whom, eg you could block swf
(flash) files on all but certain white-listed sites, for your thin clients.
It is awkward to configure every browser with proxy settings, so you'd want
to either use interception proxying or at least use a WPAD script:

http://en.wikipedia.org/wiki/Web_Proxy_Autodiscovery_Protocol

Gavin