edubuntu-users Digest, Vol 6, Issue 10

[Gavin McCullagh]

On Sun, 12 Nov 2006, neoinstinct wrote:

> Thank you for your mail, it was informative. i am using low cost
> computers from nornhtec (http://www.norhtec.com) as clients. your
> configuration works fine for 20 clients if i have double that specs i
> believe 40 clients on one server would be okay, with good data
> throughput and no bottlenecks.

I guess that's so in principal, though "double that spec" is probably not
something that one can actually achieve.  If you want a lot of people able
to login, you need to have as much RAM as possible, so 4GB (the max on a
32-Bit machine) is probably a good plan.

You can't have double that speed of cpu, but you can have 2 cpus which with
multiple users will behave similarly.  You can't get dual CPU Intel Pentium
4s, but you can get Dual cpu Intel Xeons or AMD Opterons.  The latter can
be run either as 32-Bit or 64-Bit.  Initially it would appear that using
the 64-Bit is a no-brainer, but that's not necessarily the case (eg there
is no Macromedia Flash Plugin for 64-Bit systems).

Be sure to get good fast disks, or these can be a bottleneck.  I have been
told that SCSI is substantially better than IDE with many simultaneous
accesses, though I'm unsure where S-ATA fits into this.  

I would suggest you consider RAID -- either 1 or 5, not so much for
performance but for reliability.  If one of your disks dies, you need to be
able to keep the machine running while you replace that disk.  With 40
users on the server, several days downtime while you replace a disk,
reinstall and recover from backups is really not a pleasant thought.  

Also, if you go for hardware RAID, make sure you get one which is well
supported in linux in terms of monitoring -- you want it to be able to
notify you that a disk has died.  If you can't get notification, you at
least might consider linux's MD software RAID.  There is a performance
cost, but you will have no difficulty with notifications, replacing disks,
syncing, etc.  which are all very well understood and tested.

> Do i have to use GbE for my LAN? what internet connectivity bandwidth
> would be optimal for 40 concurrent clients connected to the server?

It would probably be a good idea to have the server linked at 1Gb/sec but
it's definitely not necessary for the thin clients (which should generally
use <10Mb/sec).  Some switches offer a large number of 100Mb ports and a
few 1Gb ports.  These would usually be cheaper than fully 1Gb switches.
They also give the advantage that it's impossible for a single thin client
to use more than 10% of the bandwidth of the server.

Gavin