[NTLUG:Discuss] Building a new system

[David Neeley]

Keith,

In order to consider what kind of machine to run as
servers for QMail and Samba, you should perhaps
consider several factors:

a) How many clients will be accessing the servers?

b) What is your budget?

c) What is the importance of immediate availability of
your data?

I have seen simple Pentium boxes on Linux running very
large websites...on the order of 150K hits per day or
more (and yes, I know there are much bigger
ones...these just happened to be what I personally
observed). They were basic clone machines with 96 MB
ram, SCSI disks, and ethernet to the machine which was
serving as firewall and router.

The firewall/router in this case was a 486 with 32 MB
ram and not much for a hard drive...maybe 200 MB with
much of that unused, as I recall).

You might find you can install the same software on
both machines, with each serving as backup for the
other.

Another point: while performance of IDE disks is
increasing steadily, SCSI has a definite edge for
server use. This is primarily due to drive request
queues. That is, the CPU sends service requests to the
SCSI controller, which holds them in a small cache
until they can be served. Meanwhile, the disk is able
to remove itself from the bus until it has the
information or until the next request is made. IDE
drives are mostly sequential, one request at a time
devices. Although there are some IDE controllers with
small request queueing capability, it's a pain to be
sure that's what you're getting.

Another way you might go for one or both of these
servers is a server appliance, such as the Cobalt
Cube. You can install one of these in ten or fifteen
minutes, I understand. They are tiny boxes without
monitors, keyboards, or other direct access devices.
They are set up through your web browser. 

If you build the machines, there are several
motherboard companies which make high quality boards
and support them properly. I know there are others,
but for the last few years I have used ASUS boards
with great results. For my next machine, I'll probably
do it again. I plan to use an Imation IDE floppy drive
(Superdisk, I think they call it) that handles
standard floppies and 120 MB floppies. I'm less
interested in the 120 MB capability than I am by the
fast performance for standard ones.

You won't need much on the video side, unless these
machines will also be used as workstations. Standard
VGA will do nicely.

I'd suggest using 128 MB of ram, unless you have a
really big network to support. I don't know what ram
prices are doing after the earthquake in Taiwan last
week, but I'd imagine they are going up quite a bit.
If you have extra money left as you are building these
machines, extra RAM is always nice.

Ethernet cards are so cheap these days, even the top
brands are very affordable. If you're going to use a
10MB card, I'd suggest anything with a DEC Tulip chip.
Kingston made a very good one as of two years ago. DEC
ethernet chips have the highest throughput I've ever
seen.

If it's a 10/100 you're planning on, personally I'd
probably still go 3Com. Both these cards are fully
supported in Linux.

IMHO, you should also plan on very good UPS backup. I
have a small unit by MGE that is very nice. It is an
intelligent unit, and MGE makes a Linux driver for
bringing the system down gracefully in the event of a
power failure. Many of their units use Nicad
batteries, and are about half the size of most other
units. There is at least one vendor at the First
Saturday flea market who sells these for a lot less
than the stores, if you can even find one in the
stores. Other brands may have Linux support in their
smart units by now. I have used units by APC and Best
Power, and have had good results with them all. 

It is very instructive to read the description on the
MGE site about the different kinds of UPS design,
which ever unit you choose.

The most neglected part of the machine is the power
supply. Many people put very expensive computers
together and use the cheapest power supplies they can
find. If you have ever had a system crash because of a
power glitch that didn't affect other machines on the
same circuit, you would quickly know what I am talking
about. At the very minimum, make sure the supply is UL
rated and has a true ball bearing fan.

Several vendors make overheating alarms. The one I am
most familiar with is from PC Power and Cooling. That
one sounds an alarm if the internal temp goes above
110 degrees. Were you to have a fan failure, for
example, this would warn you. There are other
solutions if these machines will be in an area where
people are not around to notice such an alarm.

On the subject of cooling, most quality mid tower
cases have room to install a second fan. I'd highly
advise doing that.

Any cheap CD that is made to directly attach to the
IDE bus is fine. They are only used to load software
on a server, so a high quality one is overkill (unless
you want a CDR or CDRW to use for making backups. In
that case, I'd go with a SCSI unit. They have fewer
dropouts while recording. If you do that, I'd suggest
using a different SCSI adapter for the recorder. In
some if not in all cases, a high speed SCSI drive
adapter can't service the drive at full speed when
there's a slower device on the chain, which is why you
don't put an IDE CD on the same cable as a high speed
IDE hard drive).

If you're going to back up the server over ethernet to
another machine, that's fine. Otherwise, you'll
probably want a tape unit of some kind, assuming
you're not going the CDR/CDRW route. Although they're
more expensive, you'll likely get more service from a
SCSI tape unit. You'll also find SCSI devices are
easier to set up under Linux than the others. The real
cheapies use a floppy interface, and with drives as
big as we have today they can be excruciatingly slow
to back up on. 

I hope this has been instructive. Sorry for the
length, but these are areas I find most folks aren't
very familiar with unless they're network
administrators, engineers, or suchlike. Personally,
I've learned most of these things the hard way.

Best of luck.
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